Calibrating Your E Series Board
Contents
1. Figure 4 The Terminal Connections for the MIO Calibrate VI The function prototype for the MIO_Calibrate function is status MIO_ Calibrate deviceNumber calOP saveNewCal EEPROMloc calRefChan DACOchan DAC1chan calRefVolts refLoc The LabVIEW MIO Calibrate VI The MIO Calibrate VI can be used as a stand alone VI or it can be sequenced with other data acquisition VIs to perform regular calibrations within an application VI For the MIO Calibrate VI device is the number of the device which you wish to calibrate The input calibration determines which operation you wish to perform Table 7 shows the different calibration operations performed by the MIO Calibrate VI Table 7 The Calibration Operations Performed by the MIO Calibrate VI and the Corresponding calibration Value calibration Input Calibration Operation 0 Reserved 1 Load calibration contants from the EEPROM location 2 Calibrate the ADC using the internal reference voltage calibration constants in reference location 3 Calibrate the DACs using the internal voltage calibration constants in reference location 4 Calibrate the internal reference voltage You must connect a DC voltage specified by reference voltage to the analog input channel reference channel The new calibration constants are stored in reference location 5 Copy the ADC calibration constants from EEPROM location to the EEPROM load area 6 Copy the DAC calibration c2. area 8 initial load area 9 Factory calibration area for unipolar cannot write to this area 10 Factory calibration area for bipolar cannot write to this area Table 12 The Values of refLoc in the MIO_Calibrate Function Input refLoc 1 User reference area 1 default setting 2 User reference area 2 3 User reference area 3 AT MIO 16X and AT MIO 64F 5 only 4 User reference area 4 AT MIO 16X and AT MIO 64F 5 only 5 Reserved 6 Factory reference area cannot write to this area Performing a Self Calibration of the Analog Inputs of Your Legacy MIO Board Once the board is in its operating environment frequent calibrations ensure the most accurate and stable analog measurements For legacy boards this is most effectively achieved by calibrating the analog inputs ADC calibration The legacy boards calibrate the analog inputs and the analog outputs separately A separate call to the calibration function must be made to calibrate each operation Once calibrated the calibration constants are written to the CALDACs to compensate for the offsets and gain errors In addition these calibration constants may be saved to the EEPROM to be used at a later time If the calibration constants are not saved they will be lost when the computer is powered off Steps for Performing a Calibration of the Analog Inputs with LabVIEW The steps for calibrating the analog inputs of your legacy MIO board with LabVIEW are as follows Step 1 Se
3. calibration to a value of 1 If you need the calibration constants only for the time that the computer will be powered on set save new calibration to 0 If you do not save the calibration constants they will be lost when the computer is powered off or when another calibration is performed Step 3 Set EEPROM location to the area in which you wish to save the newly created calibration con stants When calibrating the analog outputs you cannot set EEPROM location to the factory calibration area because this area is read only An error will occur if this setting is used Step 4 When calibrating the analog outputs you must connect either of the analog outputs DACO and DACI to an analog input channel The channels which these outputs are connected to must be passed as DACO channel and DAC1 channel respectively If you are using an AT MIO 64F 5 these parameters are ignored because DACO is internally routed to an input channel Step 5 Set reference location to 6 if you want to use the factory reference voltage Set it to one of the user reference areas if you have already performed a calibration of the internal reference voltage and wish to use the saved calibration constants from that calibration When calibration is set to 3 the parameters reference channel and reference location are ignored Steps for Performing a Calibration of the Analog Outputs with NI DAQ To calibrate the analog outputs of your legacy MIO board using NI DAQ follow t
4. 21 Product and company names are trademarks or trade names of their respective companies 341333A 01 Copyright 1997 National Instruments Corporation All rights reserved August 1997 Necessity of Calibration Calibration refers to a procedure of reading offset and gain errors from an MIO board and updating special onboard analog calibration circuitry that will correct these errors All AT MIO boards are calibrated as shipped from the factory When the board is calibrated the calibration constants values used to update the analog calibration circuitry are stored in nonvolatile memory on the board From memory they can be loaded when needed The offset and gain errors however may drift with time and temperature As a result the calibration constants determined at the factory may not apply to the current operating environment of the board To achieve the specified accuracy of the board it must be calibrated in the operating environment For example let us calculate the voltage error that could occur from temperature drift alone Consider a situation in which we are using an AT MIO 16E 1 board calibrated at the factory at a temperature of 25 C but is now being used at 35 C We can find the approximate errors associated with temperature fluctuations from the tem perature drift specifications provided in the user manual The specifications of interest are the pregain postgain and gain offset temperature coefficients Table 1 shows the v
5. 3 Connect the DACO line to analog input channel 0 3 If your reference voltage source and your computer are floating with respect to each other connect the negative output of your reference voltage source to the AIGND line as well as to analog input channel 8 4 If your reference voltage source and your computer are floating with respect to each other connect the AISENSE line to the AIGND line as well as to the negative output of your reference voltage source ACH8 ACH1 AIGND ACH10 ACH3 AIGND ACH4 AIGND ACH13 ACH6 AIGND ACH15 DACOOUT DAC10UT EXTREF DIO4 DGND DIO1 DIO6 DGND 5V DGND DGND PFIO TRIG1 PFI1 TRIG2 DGND 5V DGND PFI5 UPDATE PFI6 WFTRIG DGND PFI9 GPCTRO_GATE O rPrrrrrrrre AOGND AOGND DGND DIOO DIO5 DGND DIO2 DIO7 DIO3 SCANCLK EXTSTROBE DGND PFI2 CONVERT PFI3 GPCTR1_SOURCE PFI4 GPCTR1_GATE GPCTR1_OUT DGND AJ oO N PFI7 STARTSCAN GPCTRO_OUT PFI8 GPCTRO_SOURCE DGND FREQ_OUT N DGND Figure 3 68 pin E Series I O Connector Steps for Performing an External Calibration in LabVIEW The following are the steps for performing an external calibration of your E Series board using the E Series Calibrate VI of La
6. Cs As a result the calibration constants written to the CALDACs are lost when the board is powered down Each time the board is used it is initialized During the initialization procedure the default calibration constants are written to the CALDACs When using LabVIEW this initialization procedure occurs the first time a data acquisition VI is called When using LabWindows CVI or a third party compiler and NI DAQ the calibration constants are loaded when the first call to NI DAQ that requires them to be loaded is made For E Series devices you can use the calibration functions to specify the default load area The default load area should be the factory EEPROM area or the user EEPROM area Once the default load area is set the calibration constants in that area will be the one written to the CALDACs This remains true even if the computer is powered down and then restarted When you calibrate the board and specify an EEPROM location in which to save the new calibration constants that EEPROM location automatically becomes the default load area If the NI DAQ software area is chosen as the default load area then the computer is powered down upon restarting the com puter the factory EEPROM area will become the default load area Remember that calibration constants saved in the NI DAQ software area are lost when the computer is powered down For legacy boards there is specific area in the EEPROM that is the default load area Any calibration constan
7. INSTRUMENTS The Software ts the Instrument Wy NATIONAL Application Note 104 Detailed Calibration Procedures for Multifunction DAQ Boards Introduction This application note describes how to calibrate your multifunction data acquisition DAQ board from National Instruments The boards that will be discussed are the AT MIO E Series Plug and Play boards the AT MIO 64F 5 the AT MIO 16F 5 and the AT MIO 16X The latter three AT MIO 64F 5 the AT MIO 16F 5 and the AT MIO 16X will be referred to as legacy boards All of the boards mentioned can be calibrated using LabVIEW or using NI DAQ with built in software routines These calibration routines can also be used to calibrate the boards from LabWindows CVI ComponentWorks or several third party compilers This application note will describe general calibration information and then will provide a step by step proce dure for calibrating the board You need to read only the step by step instructions that apply to your hardware and software configuration If you need to See Page Perform a self calibration on your E Series board 2 2 2 0 0 eee 7 Perform an external calibration on your E Series board 0 0 0 0c eee 8 Perform a self calibration on your legacy board 0 0 0 0 eee ee 15 Perform an external calibration on your legacy board 0 0 0 0 eee 18 Read frequently asked questions about calibration 0 0 cee eee eee eee
8. Performing a Self Calibration with NI DAQ The following are the steps for performing a self calibration of your E Series board with the Calibrate_E_Series function in NI DAQ Step 1 Set the calOP value to ND_SELF_CALIBRATE Step 2 If you wish to save the new calibration constants to the EEPROM set setOfCalConst to ND_USER_EEPROM_AREA If you need the calibration constants only for the time that the computer will be powered set setOfCalConst to ND_NI_DAQ SW_AREA When calOP is set to ND_SELF_CALIBRATE you cannot set setOfCalConst to ND_FACTORY_EEPROM_AREA because this area is read only If you use this setting the function will return an error The parameter calRefVolts is ignored when calOP is set to ND_SELF_CALIBRATE The final function call will look like status Calibrate_E_Series deviceNumber ND_SELF_CALIBRATE ND_USER_EEPROM_AREA CalRefVolts When performing a self calibration on the E Series boards no external connections to the board need be made Self calibrations can be performed as often as desired Frequent calibrations in no way harm the board and pro duce the most stable and accurate results Performing an External Calibration of Your E Series Board Occasionally it is necessary to perform an external calibration in which the internal reference voltage of the board is calibrated against a known source During an external calibration of the E Series boards the analog inputs and outputs are calibrated as well When
9. al The NI DAQ Calibrate_E_Series Function For the Calibrate_E_Series function deviceNumber is the number of the board that you want to calibrate This number can be found by looking in the NI DAQ Configuration Utility and finding the number in the device list next to the board of interest CalOP is the parameter that determines which operation you wish to perform Table 4 shows the possible values calOP can assume Table 4 The Possible Values Used by calOP and the Corresponding Operation calOP Value Operation Performed ND_SET_DEFAULT_LOAD_AREA Make setOfCalConst the default load area ND_SELF_CALIBRATE Perform self calibration of the device ND_EXTERNAL_CALIBRATE Perform an external calibration of the device SetOfCalConst selects the set of calibration constants used to load the CALDACs These calibration constants are either stored in the EEPROM or are contained in software by NI DAQ Table 5 shows possible values you can use for setOfCalConst Table 5 Possible Values for setOfCalConst and the Description for Each setOfCalConst Value Description ND_FACTORY_EEPROM_AREA Factory calibration area of the EEPROM This area is read only ND_NI_DAQ_ SW_AREA NI DAQ maintains calibration constants No writing of the EEPROM takes place ND_USER_EEPROM_AREA User calibration area of the EEPROM The new calibration constants will be written here Note that the values that you pass for s
10. alues for these coefficients for the AT MIO 16E 1 Table 1 Offset Temperature Coefficients for the AT MIO 16E 1 Parameter Value Pregain Offset Temperature Coefficient 5 uVv C Postgain Offset Temperature Coefficient 240 uV C Gain Offset Temperature Coefficient GOTC 20 ppm C Simply multiplying the pregain and postgain offset temperature coefficients by the temperature change of 10 C gives us possible offset errors of 50 uV and 2 4 mV for the pregain and postgain respectively To calculate the possible error caused by a change in the gain offset we must know the approximate voltage of the signal being measured and the gain setting of the MIO board Let us assume a unipolar input range of 10 V a gain of 10 and an input voltage of approximately V The gain offset is calculated as a fractional change in the gain Multiplying the GOTC by the 10 C temperature change gives a gain offset of 200 ppm Using the known gain setting of 10 the change in the gain can be cal culated as 10 200 106 V V which is 0 002 V V Now assuming an input voltage level of 1 V the overall error which may occur can be calculated as 2 0 mV The overall error caused by temperature drift is the sum of the three calculated errors 4 45 mV While an error of this magnitude is not large when compared to 1 V it can be highly detrimental when trying to measure voltages in the mV range Description of Board Level Cali
11. bVIEW Step 1 Set the operation input to 3 which is external calibrate Step 2 If you wish to save the new calibration constants to the EEPROM set calibration constants to 3 which is the user EEPROM area If you need the calibration constants only for the time that the computer will be powered on set calibration constants to 2 which is the NI DAQ software area When operation is set to external calibrate you cannot set calibration constants to the factory EEPROM area because this area is read only If you use this setting the function will return an error Step 3 The input reference voltage is the value of the external voltage that you will apply to the board Remember that this voltage is supplied by a high precision voltage supply Steps for Performing an External Calibration with NI DAQ The following are the steps for performing an external calibration of your E Series board using the Calibrate_E_Series function of NI DAQ Step 1 Set the calOP value to ND_LEXTERNAL_CALIBRATE Step 2 If you wish to save the new calibration constants to the EEPROM set setOfCalConst to ND_USER_EEPROM_AREA If you need the calibration constants only for the time that the computer will be powered on set setOfCalConst to ND_NI_LDAQ SW_AREA When calOP is set to ND_EXTERNAL_CALIBRATE you cannot set setOfCalConst to ND_FACTORY_EEPROM_AREA because this area is read only If you use this setting the function will return an error Step 3 The parame
12. bration Components The AT MIO E Series boards the AT MIO 64F 5 the AT MIO 16F 5 and the AT MIO 16X boards all have nonvolatile memory EEPROMs used to store the calibration constants The calibration constants are written to calibration digital to analog converters CALDACs The CALDACs output an analog voltage proportional to the calibration constants written to them These voltages are used to modify the incoming or outgoing analog voltage path in a way which will cancel the offset and gain errors Depending on your board there may be CALDACs specifically for unipolar analog input bipolar analog input unipolar analog output or bipolar analog output Consult the user manual for your board for a more detailed description of the calibration registers In the case of E Series boards you should consult the E Series Register Level Programming Manual for a complete description of the calibration registers Note A thorough knowledge of the CALDACs or calibration registers on your board is NOT required to calibrate the board NI DAQ manages all the register level communication within the calibration functions The EEPROMs on the boards can be used to store different sets of calibration constants When the board is cal ibrated at the factory the calibration constants are stored in a read only portion of the EEPROM Until the board is self calibrated by the user these calibration constants will be the set that is written to the CALDACs upon ini t
13. bration Constants The following are the steps for changing the default calibration constants on your E Series board using LabVIEW Step 1 Set the operation input to 1 which is set default load area Step 2 Set the calibration constants input to the area that you wish to become the default load con stants Values of 1 2 or 3 are all valid For more information on the loading of the calibration constants see the section entitled Calibration Constant Loading Using the Calibrate_E_Series Function to Change the Default Calibration Constants The following are the steps for changing the default calibration constants on your E Series board using NI DAQ Step 1 Set the calOP parameter to ND_SET_DEFAULT_LOAD_AREA Step 2 Set the setOfCalConst parameter to the area that you wish to become the default load constants Values of ND_FACTORY_EEPROM_AREA ND_NI_DAQ_ SW_AREA and ND_USER_EEPROM_AREA are all valid The section entitled Calibration Constant Loading further discusses how the calibration constants are loaded Calibrating Your Legacy Board The VI used to calibrate your AT MIO 64F 5 AT MIO 16F 5 or AT MIO 16X in LabVIEW is the MIO Calibrate VI NI DAQ uses the function MIO_Calibrate to calibrate the boards Figure 4 shows the terminal connections for the MIO Calibrate VI reference location DACI channe DACI channe device calibration gave new calibration EEPROM location reference channe device out status
14. calibrate the internal reference voltage of your board This is the voltage that is used as a known reference when calibrating the analog input voltages or generating the analog output voltages You should calibrate the internal reference voltage if it has not been calibrated for more than a year or if the board will be used at extreme temperatures However you can also calibrate the internal reference voltage as often as needed to satisfy calibration documentation requirements When calibrating the internal reference voltage it is important to use a high precision voltage supply The voltage supply must have an accuracy greater than the accuracy of the analog to digital converter of the MIO board The required precision of the source depends on the accuracy of the board you are calibrating If you have a 16 bit board then the accuracy of the source should be 10 ppm and for a 12 bit board it should be 50 ppm If your source is not accurate enough you will receive an error message during calibration and the calibration will not converge Connecting the High Precision Voltage Source When calibrating the internal reference voltage you must connect the high precision voltage source to the board This is done by connecting the positive lead of the supply to the positive side of the analog input channel specified by reference channel and the negative lead of the supply to the negative side of the input channel Figure 5 provides the pinouts for the l
15. cate 4 How accurate must my external source be The source must be more accurate than the analog to digital converter on the board When calibrating a 12 bit board your source should be at least 50 ppm 0 005 accurate When calibrating a 16 bit board your source should be at least 10 ppm 0 001 accurate For example when supplying an external 10 V i e full scale cal ibration voltage to a 12 bit board the source must be accurate to within 500 uV However when supplying the same signal to a 16 bit board the source must be accurate to within 100 uV 5 What is the benefit of doing on site calibration The benefit of doing an on site internal calibration is that you remove any gain and offset errors from the analog circuitry The benefit of doing an on site external calibration is that you remove any reference drift from the analog circuitry 6 Does my board have to be set up in differential mode The VIs and NI DAQ functions take control of the board during the calibration procedure so it does not matter what measurement mode is being used In other words the precalibration settings could be anything The post calibration settings are not necessarily returned to the precal settings so it is left up to the user to set them appropriately once the calibration is complete 7 What if I want to calibrate only analog output The E Series software calibrates both analog input and output at the same time while the legacy MIO software re
16. e you wish to save the newly created cali bration constants Table 2 and Table 3 show a list of the possible values for operation and calibration constants and the description of each Table 2 Possible Values for the Operation Input of E Series Calibrate operation Input Description 0 No change default input 1 Set default load area default setting 2 Perform a self calibration 3 Perform an external calibration Table 3 Possible Values for the Calibration Constants Input of E Series Calibrate calibration constants Input Description 0 No change default input 1 Factory EEPROM area default setting 2 NI DAQ software area 3 User EEPROM area The reference voltage input indicates the voltage of the external voltage supply you are using to perform an external calibration When performing an external calibration you must use a high precision voltage supply This will be discussed further in the section entitled Using the E Series Calibrate VI to Perform an External Calibration The error input or output describes error conditions before or after the execution of the VI If you are using the E Series Calibrate VI as a stand alone VI you do not need to use the error in input When using the VI inside of an application to perform routine calibrations you can use the task ID and the error in to sequence your VIs For more information see the LabVIEW Data Acquisition Basics Manu
17. egacy boards Al GND ACHO ACH1 ACH2 ACH3 ACH4 ACH5 ACH6 ACH7 Al SENSE DAC1 OUT AO GND ADIOO ADIO1 ADIO2 ADIO3 DIG GND 5V EXTSTROBE EXTGATE SOURCE1 OUT1 GATE2 SOURCES OUT5 Al GND ACH8 ACH9 ACH10 ACH11 ACH12 ACH13 ACH14 ACH15 DACO OUT EXTREF DIG GND BDIOO BDIO1 BDIO2 BDIO3 5V SCANCLK EXTTRIG EXTCONV GATE1 EXTTMRTRIG OUT2 GATES FOUT Figure 5 50 Pin Legacy Board I O Connector Steps for Performing a Calibration of the Reference Voltage with LabVIEW The following steps can be used to calibrate the internal reference voltage of your legacy MIO board using LabVIEW Step 1 Set the calibration value to 4 Step 2 The parameter reference channel is the analog input channel that the calibration voltage is con nected to This is the voltage from the high precision voltage supply Step 3 Set reference voltage to the value of the DC calibration voltage connected to reference channel Step 4 To save the calibration constants set reference location to one of the user reference areas The parameters EEPROM location DACO channel and DAC1 channel are ignored when calibration is set to 4 19 Steps for Performing a Calibration of the Reference Voltage with NI DAQ The procedure for calibrating the internal reference voltage of your MIO legacy board wit
18. etOfCalConst and calOP are constant definitions defined in header files The particular header file depends upon the compiler or development environment you are using Consult the NI DAQ User Manual for information regarding specific compilers If you are using LabWindows CVI the con stants are defined in the DATAACQ H file CalRefVolts is the DC calibration voltage that you will connect to the board to calibrate the internal reference voltage This voltage must come from a high precision voltage source Calibration of the internal reference volt age will be discussed in the section entitled Using Calibrate_E_ Series to Calibrate the Internal Reference Voltage Performing a Self Calibration on Your E Series Board Once the board is in its operating environment frequent calibration ensures the most accurate stable and repeatable measurements A self calibration is the most effective way to do this During a self calibration both the analog inputs and the analog outputs are calibrated The internal reference voltage is not calibrated during a self calibration A self calibration will create a new set of calibration constants by performing a pregain offset a postgain offset and a gain error calibration as seen in Figure 1 Once the calibration is performed the new calibration constants are loaded to the CALDACs on the board If you wish these calibration constants can be saved to the EEPROM where they can be reloaded when necessary It is impor
19. h NI DAQ is as follows Step 1 Set the calOP value to 4 Step 2 The parameter calRefChan is the analog input channel that the calibration voltage is connected to This is the voltage from the high precision voltage supply Step 3 Set calRefVolts to the value of the DC calibration voltage connected to calRefChan Step 4 To save the calibration constants set refLoc to one of the user reference areas The parameters EEPROMloc DACOchan and DAC1chan are ignored when calOP is set to 4 When calibrating the internal reference voltage you must connect the high precision voltage source to the board This is done by connecting the positive lead of the supply to the positive side of the analog input channel specified by calRefChan and the negative lead of the supply to the negative side of the input channel Performing a Complete Calibration of Your Legacy MIO Board If you wish to perform a complete calibration of your legacy board you must call the calibration routine three times You must first calibrate the internal reference voltage as discussed above and then calibrate the analog input and the analog output The order of calibrating the input and the output does not matter but the internal reference voltage must be calibrated first This applies regardless of whether you are using LabVIEW or NI DAQ Calibration Constant Loading The E Series boards and the legacy boards discussed in this application note do not have memory for the CALDA
20. hese steps Step 1 Set the calOP value to 3 Step 2 If you wish to save the new calibration constants to the EEPROM set saveNewCal to a value of 1 If you need the calibration constants only for the time that the computer will be powered on set saveNewCal to 0 If you do not save the calibration constants they will be lost when the computer is powered off or when another calibration is performed Step 3 Set EEPROMloc to the area in which you wish to save the newly created calibration constants When calibrating the analog inputs you cannot set EEPROM loc to the factory calibration area because this area is read only An error will occur if this setting is used Step 4 When calibrating the analog outputs you must connect either of the outputs DACO and DAC1 to an analog input channel The channels which these outputs are connected to must be passed as DACOchan and DACIchan respectively If you are using an AT MIO 64F 5 these parameters are ignored because DACO is internally routed to an input channel Step 5 Set refLoc to 6 if you want to use the factory reference voltage Set it to one of the user reference areas if you have already performed a calibration of the internal reference voltage and wish to use the saved calibration constants from that calibration When calOP is set to 3 the parameters calRefChan and calRefVolts are ignored Performing an External Calibration of Your Legacy MIO Board Occasionally it is necessary to
21. hould be calibrated if the board is to be used in extreme temperatures or if it has not been calibrated for more than a year A high precision voltage supply is necessary when calibrating the inter nal reference voltage 341333A 01 Aug97
22. ialization of the board When the board is calibrated in its working environment you have the choice to save the newly generated calibration constants to a location in the EEPROM When this is done these calibration con stants will be written to the EEPROM as well as to the CALDACs Since the CALDACs do not have memory each time the computer is powered off the CALDACs lose their val ues As aresult the calibration constants must be re loaded each time the board is powered up and used NI DAQ automatically loads the CALDACs with the default calibration constants the first time a function is called which requires them In the case of LabVIEW the CALDACs are loaded when the first virtual instrument VJ that uses data acquisition is loaded The default calibration constants may be the factory constants or constants saved in a user area of the EEPROM After a calibration if the constants are saved to the EEPROM the newly created calibration constants become the default calibration constants Calibration constant loading will be discussed in the section Calibration Constant Loading later in this application note You can also use the calibration functions to change the default calibration constants This will be discussed in a subsequent section Calibration Order Using the calibration functions you can instruct the board to perform a self calibration or calibrate the internal reference voltage When a calibration is performed the board will determ
23. ine the calibration constants for the analog input or the analog output or the internal reference voltage and store these constants in the EEPROM Once the self calibration is performed the set of calibration constants that was determined will become the default calibration constants and will be automatically loaded when any NI DAQ function or LabVIEW data acquisition VI is called The calibration constants need to be written to the CALDACs to compensate for the pregain and postgain offset and the gain error During the calibration procedure these error sources are calibrated in a specific order Figure 1 shows the offset calibration order Pregain Offset y Reference Voltage Error Postgain Offset Optional y Gain Error Figure 1 The Self Calibration Method The pregain offset is the voltage difference between the true voltage and the measured voltage at the input of the amplifier This offset is measured by grounding the inputs to the programmable gain instrumentation amplifier PGIA This offset is measured at different gains and once calibrated should be independent of the gain setting Similarly the postgain offset is the difference between the true and measured voltage at the output of the ampli fier This offset is measured by grounding the input of the PGIA and measuring the output The circuitry is adjusted until this output is as small as possible The gain err
24. onstants from EEPROM location to the EEPROM load area The input save new calibration determines whether the new calibration constants are saved to the EEPROM The value of EEPROM location and reference location determine where the new calibration constants are saved When the ADC or the DACs are calibrated the calibration constants for the operation are saved in the EEPROM location When the internal reference voltage is calibrated the calibration constants are saved in the reference location The other parameters reference channel DACO channel DAC1 channel and reference voltage are used only during certain calibration procedures These parameters will be discussed during the step by step pro cedures in the following sections Table 8 shows the valid values of EEPROM location and Table 9 shows the values of reference location Table 8 The Values of EEPROM Location in the MIO Calibrate VI Input EEPROM Location 0 Reserved 1 User calibration area default setting 2 User calibration area 2 3 User calibration area 3 4 User calibration area 4 5 User calibration area 5 load area for AT MIO 16F 5 6 User calibration area 6 AT MIO 16X and AT MIO 64F 5 only vs User calibration area 7 AT MIO 16X and AT MIO 64F 5 only 8 Load area for AT MIO 16X and AT MIO 64F 5 9 Factory calibration area for unipolar AT MIO 16X and AT MIO 64F 5 only 10 Factory calibration area f
25. or bipolar AT MIO 16X andAT MIO 64F 5 only 11 Factory calibration area for AT MIO 16F 5 Table 9 The Values of reference location in the MIO Calibrate VI Input reference location 0 Reserved 1 User reference area default setting 2 User reference area 2 3 User reference area 3 AT MIO 16X and AT MIO 64F 5 only 4 User reference area 4 AT MIO 16X and AT MIO 64F 5 only 5 Reserved 6 Factory reference area cannot write to this area The NI DAQ MIO_ Calibrate Function For the MIO_Calibrate function deviceNumber is the number of the device you wish to calibrate The parameter calOP determines which operation you wish to perform Table 10 shows the different calibration operations performed by the MIO_ Calibrate function Table 10 The Calibration Operations Performed by the MIO_Calibrate Function and the Corresponding calOp Value calOP Value Calibration Operation 1 Load calibration constants from EEPROMloc 2 Calibrate the ADC using the internal reference voltage calibration constants in refLoc 3 Calibrate the DACs using the internal voltage calibration constants in refLoc 4 Calibrate the internal reference voltage You must connect a DC voltage of calRefVolts to the analog input channel calRefChan The new calibration constants are stored in refLoc 5 Copy the ADC calibration constants from EEPROM Ioc to the EEPROM load area 6 Copy the DAC calibration con
26. or is the difference between the gain setting and the measured gain This is calibrated by measuring the internal reference voltage at a gain of 1 and adjusting the gain until the measured voltage is equal to the value of the reference voltage stored in the EEPROM Figure 1 shows that the gain error is always calibrated after the postgain offset which in turn is always calibrated after the pregain offset The pregain and postgain offsets and the gain error are all adjusted using the CALDACs on the board Each CALDAC must be loaded with a value that will minimize the errors caused by these sources These values which update the CALDACs to minimize the errors are the calibration constants There is a final error source the difference between the internally stored reference voltage and its actual value The calibration functions can be used to adjust this parameter as well However to calibrate this voltage you need a high precision voltage source Using the calibration functions provided with NI DAQ and Lab VIEW there are three operations you can perform You can 1 calibrate the analog circuitry 2 change the default load area and 3 calibrate the internal reference voltage For the AT MIO 16X the AT MIO 16F 5 and the AT MIO 64F 5 you must specify whether you are per forming an analog input or an analog output calibration when calibrating the analog circuitry For the E Series boards the self calibration procedure calibrates both the analog inpu
27. performing an external calibration it is necessary to use a high precision voltage source The source must be more accurate than the analog to digital converter on the board When calibrating a 12 bit board your source should be at least 50 ppm 0 005 accurate When calibrating a 16 bit board your source should be at least 10 ppm 0 001 accurate For example when supplying an external 10 V i e full scale calibration voltage to a 12 bit board the source must be accurate to within 500 uV However when supplying the same signal to a 16 bit board the source must be accurate to within 100 uV Connecting the High Precision Voltage Source When performing an external calibration you must connect an external reference voltage to the board The connections are slightly different for 16 bit boards than for 12 bit boards Table 6 describes the connections that must be made for each type of E Series board and Figure 3 shows the 68 pin I O connector Table 6 Necessary Connections to Your E Series Board before External Calibration 12 Bit E Series Devices 16 Bit E Series Devices 1 Connect the positive output of the reference 1 Connect the positive output of your reference voltage source to the analog input channel 8 voltage source to analog input channel 0 2 Connect the negative output of your reference 2 Connect the negative output of your reference voltage source to the AISENSE line voltage source to analog input channel 8
28. quires individual calls for analog input or output 21 8 What if I get errors during calibration 10401 Unknown Device This means that the device number specified is not defined in the NI DAQ Configuration Utility 10403 Device Support Error This means that the action specified is not supported for the device for example trying to do an E Series calibration on a legacy board 10801 Calibration Error This can mean that the board EEPROM needs to be repaired 10842 Hardware Error The call was appropriate for the device but the response from the device is not consistent with the device functionality Repeated errors of this type can mean something on the board is physically damaged Conclusion LabVIEW and NI DAQ include functions that calibrate your E Series board and certain legacy boards With these functions you can calibrate the analog inputs the analog outputs and the internal reference voltage These functions generate calibration constants that are used to update CALDACs The CALDACs output an analog voltage that will compensate for offset and gain errors These calibration constants can be saved in nonvolatile memory to be recalled when necessary In general routine calibration of the analog inputs and analog outputs produce the most accurate and stable results These calibrations can be performed periodically or can be made part of your application for calibrating on a regular basis The internal reference voltage s
29. stants from EEPROM Ioc to the EEPROM load area The value of saveNewCal determines whether the new calibration constants are saved to the EEPROM The value of EEPROM loc and refLoc determine where the new calibration constants are saved When calibrating the ADC or the DACs the calibration constants are saved in EEPROMloc When calibrating the internal reference voltage the calibration constants are saved in refLoc The other parameters calRefChan DACOchan DACI1chan and calRefVolts are used only during certain calibration procedures These parameters will be discussed during the step by step procedures in the following sections Tables 11a and 11b show the valid values of EEPROM loc and Table 12 shows the values of refLoc Table lla The Values of EEPROMloc in the MIO_Calibrate Function Input EEPROMloc for AT MIO 16F 5 1 User calibration area 2 User calibration area 2 3 User calibration area 3 4 User calibration area 4 5 User calibration area 5 initial load area 6 Factory calibration area cannot write to this area Table 11b The Values of EEPROMloc in the MIO_Calibrate Function Input EEPROMloc for AT MIO 64F 5 and 16X 1 User calibration area 1 2 User calibration area 2 3 User calibration area 3 4 User calibration area 4 5 User calibration area 5 6 User calibration area 6 7 User calibration area 7 8 User calibration
30. t and output portions of the analog circuitry For a complete description of how these functions are used see the sections entitled Calibrating Your E Series Board and Calibrating Your Legacy Board Calibrating Your E Series Board The functions used to calibrate the E Series boards are called E Series Calibrate and Calibrate_E_Series for LabVIEW and NI DAQ respectively Figure 2 shows the terminal connections for the E Series Calibrate VI task ID Zeri task ID out operation calibration constanta _ eror out efor in no error reference voltage Figure 2 The Terminal Connections for the E Series Calibrate VI The function prototype for the Calibrate_E_Series function is status Calibrate_E_Series deviceNumber CalOP setOfCalConst CalRefVolts The LabVIEW E Series Calibrate VI The E Series Calibrate VI can be used alone to perform a one time calibration or it can be used in an application VI to perform routine calibrations The input task ID can be a task ID created by any of the configuration VIs such as AI Configure or it can be the device number of the device you wish to calibrate You can find the device number for your board by opening the NI DAQ configuration utility and locating the number beside the device of interest in the device list The operation input to the VI specifies which type of operation you wish to perform The calibration constants input determines which calibration constants you wish to use or wher
31. t the device value to the number of the device you wish to calibrate Step 2 Set the calibration value to 2 which is to calibrate the ADC Step 3 If you wish to save the new calibration constants to the EEPROM set save new calibration to a value of 1 If you need the calibration constants only for the time that the computer will be powered on set save new calibration to 0 If you do not save the calibration constants they will be lost when the computer is powered off or when another calibration is performed Step 4 Set EEPROM location to the area in which you wish to save the newly created calibration con stants 1 4 6 7 When calibrating the analog inputs you cannot set EEPROM location to the factory calibration area because this area is read only An error will occur if this setting is used Step 5 Set reference location to 6 if you want to use the factory reference voltage Set it to one of the user reference areas 1 4 if you have already performed a calibration of the internal reference voltage and wish to use the saved calibration constants from that calibration The inputs DACO channel DAC1 channel reference channel and reference voltage are all ignored when cal ibration is set to 2 No external connections are necessary when performing a calibration of the analog inputs Steps for Performing a Calibration of the Analog Inputs with NI DAQ The following are the steps for calibrating the analog inputs of your legacy MIO board
32. tant to save the calibration constants if they will be needed after the board has been powered down If the calibration constants are not saved to the EEPROM they will be lost when the computer is powered down Steps for Performing a Self Calibration in LabVIEW The following are the steps for performing a self calibration of your E Series board using the E Series Calibrate VI in LabVIEW Step 1 Set the operation input to 2 which is self calibrate Step 2 If you wish to save the new calibration constants to the EEPROM set calibration constants to 3 which is the user EEPROM area Once in the user EEPROM area you can load the constants when needed If you need the calibration constants only for the time that the computer will be powered set calibration constants to 2 which is the NI DAQ software area With this setting NI DAQ will maintain the calibration constants until another calibrations performed or the computer is powered down When operation is set to 2 you cannot set calibration constants to 1 which is the factory EEPROM area because this area is read only If you use this setting the VI will return an error The input reference voltage is ignored when operation is set to 2 When performing a self calibration no external connections need to be made to the board Self calibrations can be performed as often as desired Frequent calibrations in no way harm the board and produce the most stable and accurate results Steps for
33. ter calRefVolts is the value of the external voltage that you will apply to the board Remember that this voltage is supplied by a high precision voltage supply The function call to NI DAQ will look like the following status Calibrate_E_Series deviceNumber ND_EXTERNAL_CALIBRATE ND_USER_EEPROM_AREA CalRefVolts Changing the Default Calibration Constants of Your E Series Board Once a calibration has been performed and the calibration constants have been saved there are two sets of usable calibration constants in the EEPROM One is the set created at the factory and the other is the set created by the user calibration It is possible to calibrate the board again and maintain a set of calibration constants in NI DAQ software Any set of constants maintained in NI DAQ will be lost when the computer is powered down Occasionally it may be desirable to change the calibration constants being used by the board For example you may have one set of calibration constants that are used when the board is in a high temperature environment and the factory constants that are used at room temperature You can change the calibration constants used with the calibration functions provided by LabVIEW and NI DAQ Once the calibration constants are changed the new set of calibrations constants become the default constants The default constants are automatically loaded when the board is initialized Using the E Series Calibrate VI to Change the Default Cali
34. ts you save in that area will become the default calibration constants upon board initialization With the calibration functions you can copy constants from one area of the EEPROM to another 20 NIST Traceable Calibration Certificate You can obtain a NIST traceable calibration certificate from National Instruments with your E Series board To do this simply contact National Instruments and request to send your board in for recalibration including a certificate Frequently Asked Questions Regarding Calibration 1 How often should I calibrate my board You should perform an internal calibration as often as possible i e once a day or before each measurement set in order to ensure maximum accuracy You should perform an external calibration if the onboard reference has not been calibrated for more than a year Also if the board is operating in an environment more than 10 C different from its last calibration environment and the estimated drift due to temperature is unacceptable for your application then you should perform an external calibration Of course you can perform external calibrations as often as required to meet any calibration documentation requirements 2 What voltage should I apply for an external calibration Typical values are between 5 00 and 9 99 V for a calibration at a gain of 1 3 How can I get a calibration certificate You can return the board to National Instruments and request recalibration with a certifi
35. ts when they are calibrated in their operating environment The calibration constants for the analog output calibration are stored in an area of the EEPROM separate from the calibration constants for the analog input calibration It is not necessary to calibrate both the analog inputs and the analog outputs Simply calibrate the circuitry of the operation you wish to perform Connections to Make Before Calibrating Analog Outputs When you are using the AT MIO 16X or the AT MIO 16F 5 you must make external connections to calibrate the analog outputs For the AT MIO 16X you must connect DACO or DAC 1 to the positive side of the differential analog input channel specified by DACO channel or DAC1 channel You must then connect the AOGND pin to the negative side of the differential analog input channel When calibrating the AT MIO 16F 5 you must connect DACO or DAC1 to the negative side of the differential analog input specified by DACO channel or DAC1 channel The AOGND pin must be connected to the positive side of the analog input If these connections are not made correctly the calibration will not converge and an error will result Steps for Performing a Calibration of the Analog Outputs with LabVIEW The following steps can be used when performing a calibration of the analog outputs of your legacy MIO board using LabVIEW Step 1 Set the calibration value to 3 Step 2 If you wish to save the new calibration constants to the EEPROM set save new
36. using the NI DAQ library Step 1 Set the calOP value to 2 Step 2 If you wish to save the new calibration constants to the EEPROM set saveNewCal to a value of 1 If you need the calibration constants only for the time that the computer will be powered on set saveNewCal to 0 If you do not save the calibration constants they will be lost when the computer is powered off or when another calibration is performed Step 3 Set EEPROMloc to the area in which you wish to save the newly created calibration constants When calibrating the analog inputs you cannot set EEPROMloc to the factory calibration area because this area is read only An error will occur if this setting is used Step 4 Set refLoc to 6 if you want to use the factory reference voltage Set it to one of the user reference areas if you have already performed a calibration of the internal reference voltage and wish to use the saved calibration constants from that calibration The parameters calRefChan DACOchan DAC1chan and calRefVolts are all ignored when calOP is set to 2 No external connections are necessary when performing a calibration of the analog inputs In general the final function call is as follows status MIO_Calibrate deviceNumber 2 1 EEPROMloc calRefChan DACOchan DACIchan calRefVolts 6 Performing a Self Calibration of the Analog Outputs of Your Legacy MIO Board Similar to analog inputs the legacy boards produce the most stable analog outpu
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