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1. CHIRON Exposure Meter Version 2 Author Andrew Szymkowiak Yale University Last update July 27 2015 File prj bme chiron EM EMv2 doc 1 Short description and hardware The main functions of the Chiron Exposure Meter from now on expm for short is to calculate the photon weighted mean time for exposures and to stop the exposures so that a targeted level of signal is collected Its hardware consists of three main components a Hamamatsu PMT which views a small amount of the light after the spectrograph collimator through a pick off mirror and a fiber an electronics box which takes the drive signal for the shutter and outputs logic signals to the parallel port of the third component a PC running Linux SMA fiber from GHIRON EM software Ethernet socket connection to GHIRON SW Serial connection Parallel port Power supply 5V Shutter signal Shutter from Torrent signal box Figure 1 Block diagram of EM hardware and connections Figure 1 shows main components of the EM and their connections The PMT is Hamamatsu H9319 01 It is housed in a light tight metal box with a green filter Chroma D545 80x in front of it The fiber is scotched into the box no connector The device is powered by 5V Digitized counts are read by the computer which also turns the high voltage HV ON or OFF There is no built in over light protection the PMT will be damaged if exposed to ambient light w2. em_avgsq dbs flush em_prdsum dbs flush em_netint dbs flush em_mnwob dbs flush em_mnwb The contents of the add_keys file is sent to the database server when the program is started to prepare the system to deal with the FITS variables when they are set expmeter expmeter EXPFITS4 more del_keys dbs delete em_timopn dbs delete em_timcls dbs delete em_numsmp dbs delete em_avg dbs delete em_avgsq dbs delete em_prdsum dbs delete em_netint dbs delete em_mnwob dbs delete em_mnwb fits key delete emtimopn fits key delete emtimcls fits key delete emnumsmp fits key delete emavg fits key delete emavgsq fits key delete emprdsum fits key delete emnetint fits key delete emmnwob fits key delete emmnwb The del_keys file is supposed to be sent when the program exits cleanly in order to cleanly remove the expmeter 5 variables from the FITS headers Currently the program apparently does not ever exit cleanly so that the expmeter items stay in the headers but with zero values If desired the del_keys file could be streamed into the database socket by hand if you want those items to not appear in the headers Here is the current contents of the pf file for the early termination client expmeter expmeter EXPPFFILES more exptermb1 pf 2110 ctioe1 ctio noao edu 5415 10 100 10 1000 The first parameter is the port number on which the client will listen for threshold setting commands The second and thi
3. file Until this is written reading the source code will be the best way to find these details Computer requirements The current generation of the h w requires a Linux computer with a serial and parallel port The parallel port interface was chosen as an inexpensive way to get an interrupt tied to an external logic signal and with a second input available to detect current shutter signal level status As this legacy interface is vanishing from modern motherboards we might want to consider other options for instance just obtaining the shutter transition times from the Torrent Another option would be to get two GPIO inputs some other way there are inexpensive PCI cards and embedded Linux system boards Raspberry Pi BeagleBone Black w GPIO pins though would need CMOS instead of TTL levels The custom parallel port driver is a modification of the ppdev driver supplied with the 2 6 32 Linux kernel We have used Scientific Linux 6 and a CentOS distribution both of these systems are redistributed versions of the Red Hat Enterprise Linux 6 system The ppdev interrupt routine was modified to place the state of the shutter level signal and the time into a ring buffer when the interrupt is triggered by the signals generated at the shutter signal edges A new ioctl PPGETINTTIME was added to the driver to be used in the main to fetch entries from the ring buffer This modified driver is in the directory rpmbuild BUILD kermel 2 6 32 431 el6
4. first one port num is the port on which expmsrv will start listening for connections from clients The second num_pmt_samples is probably not being used at the moment this should be remedied in a future software revision The PMT intrinsically samples at 10 ms intervals and a command sent at startup has it do some binning Having this set to 10 means the program is receiving binned samples every 0 1 seconds The third binning_size is the additional binning used for the samples logged to the cnts file and sent to the plot client 20 corresponds to 2 second bins The fourth ser_time_offset could be used to remove a skew from the serial sample time assignments Currently I do not know what value this should have and leave it at zero The fifth avg_size is how many bins are combined to form the averages used to estimate the pre and post exposure backgrounds The sixth threshold and seventh thresh_cntr_max are used for tripping off the HV in this example 10 consecutive samples exceeding 10 million counts will shut the HV off Here is the contents of the expfits4 pf file expmeter expmeter EXPPFFILES more expfits4 pf ctioe1 ctio noao edu 5415 These items are merely the address and port number of where to make the socket connection for sending the database commands to set the values of the FITS header values This program also reads files named add_keys and del_keys from the current directory not yet the pf directory
5. ient can plot the light curve from the PMT Its name starts with expplt and it has 4 input boxes to set the limits of the plot and a button to choose to plot the log of the intensities This display is currently mainly for debug use as it replots all the points upon the arrival of each new sample and cannot keep up with a small bin size or many points in the plot We hope to write a better plot client some day A description of the photon weighted mean time calculations and FITS variable contents might be placed here in the interim an examination of the source code will probably serve to provide details of these calculations and interfaces 4 Software details Both the main and some of the clients look for an environment variable named EXPMPFDIR which tells them where to find the parameter files for setting various things When this was written the env var is set at login time to point to home expmeter EXPPFFILES The cshrc also sets two other environment variables LD_LIBRARY_PATH which is loaded with a library that the clients need and EXPMHOST which tells the clients where to look for the expmsrv main The pf parameter file for the expmsrv is named expm pf here is the current contents expmeter expmeter EXPPFFILES more expm pf 2000 port_num 10 num_pmt_samples must correspond to value on P cmd sent to PMT 20 binning_size 0 ser_time_offset 10 avg_size 10000000 threshold 10 thresh_cntr_max The
6. ith HV ON The EM software switches HV OFF if the detected flux exceeds a certain threshold Pe ee ge GomeanaoR 7 CHIRON Green Filter 1 4 PRESCALER 4 bit counter 140 MHz Transmission 4 bit counter 140 MHz Optical density x10 RS 232C EPEAT A ell ase tae al PERS i o O o O 300 400 500 600 700 800 900 1000 1100 IN OUT Rx Tx 5V GND USER IO INTERFACE a Figure 2 Block diagram of the PMT circuits left and the transmission of the filter right This documentation consists of five sections an overview of the system a users guide a more detailed description of the 2 processing details of the software including descriptions of the interfaces between expm components and those to the rest of the Chiron system and an estimate of the sensitivity of the system and an appendix with miscellaneous details not yet woven into the text 2 Overview The drive signal for the Chiron shutter goes true for the duration of the exposure the shutter logic box makes a positive going pulse at both edges of the shutter signal in order to trigger the parallel port and also passes the signal to another input line of the parallel port so that the program can sense the polarity of the transition The Linux system has a custom version for the parallel port driver which records the system clock in the interrupt routine that is triggered by the shutter edge pulses The software consists
7. linux 2 6 32 431 el6 i686 drivers char ppdev in the expmeter user s home directory A new kernel and modules is created by doing a make make install make modules_install series of commands The boot grub grub conf file is then modified to point to the new kernel Exposure meeting sensitivity probably just a copy of Julien s memo with the calcs or a pointer to that memo and info from power meter measurements during the re commisioning Miscellaneous facts not yet woven into text Another part of the hardware is a 5 volt power supply for the Hamamatsu PMT The 5 volts is connected through a 4 pin circular Tyco connector The positive voltage lead first passes through a loop blue wire on the PMT side of the connector before being sent to the PMT this was to allow for the future installation of a safety switch for instance on the Chiron lid to shut off the PMT power when opening the spectrometer The shutter logic box has three connections a three pin Lemo connector that receives a copy of the Chiron shutter signal third wire is for power for an optical isolator a DB 25 connector that delivers the signals to the parallel port and a USB connector which is just used to deliver 5 volt power to the circuitry inside the box Insert circuit diagram and PCB board layouts here This document does not cover the EM optics inside CHIRON that directs part of the light into EM fiber See Section 3 7 and Figure 14 in the In
8. of the main handler expmsrv which reads from the expm hardware and a number of client programs which connect to a socket server in expmsrv to get access to the data The Hamamatsu PMT digitizes the light level and outputs a stream of counts to the serial port of the Linux box with 0 1s cadence The main program contains a tight loop which uses a non blocking read to look for the current sample from the PMT when the read returns a sample the program assigns the current system time to that sample Since there can be some latency in this time assignment the times assigned to the serial samples are likely not as accurate as those assigned to the shutter edges The expmsrv program must be installed to run as root since it must directly attach to the parallel and serial ports When the program is started it initializes the PMT including turning on the high voltage HV and starts looking at the incoming samples If a programmable number of samples consecutively exceeds a threshold the HV will be tripped off to protect the PMT The expmsrv program opens three files with timestamp names in the form yyyymmddhhmmss The arriving samples are binned and are continuously written to the cnts file Information about each exposure is written to the log file In addition copies of the information that is sent for populating the FITS headers is written to the fitinf file When expmsrv detects a shutter open it records the opening time and begins acc
9. quest to terminate the exposure at the appropriate time 3 User guide The expmsrv computer is named expmeter60 We are working on some cron jobs which will kill and start expmsrv and the FITS and early term clients at noon every day We ll also place here the name of scripts to kill and restart the three main programs If there are problems do a ps aux grep exp more and look for the process ids for processes whose names start expmsrv expfits and expterm and kill SIGINT those processes SIGINT rather than KILL because the expmsrv can detect the interrupt and shutdown the HV cleanly One of the other utility clients is the status GUI the name starts with expst This GUI has an indicator at the top for the HV status three lines for status messages and three buttons The indicator can show as blue for unknown only just after status client has been started red for HV off and green for HV on The update button will ping the expmsrv main 3 and update the indicator The HV ON and HV OFF buttons are self explanatory The button labelled rebase is not operational yet The main purpose for this GUI is to detect whether the safety check has tripped off the PMT HV and to provide manual control of the HV for instance if the system is going to be worked on Possibly these functions should just be added into the Chiron control GUI rather than requiring this separate client to be running Another utility cl
10. rd rows set the server and port number where the system will send the set exposure time commands to terminate the exposure The fourth row sets a variable named binsize this must correspond to the sampling being done in the PMT and is used to know how to use the slope in sample number to predict an exposure time in seconds The fifth row sets a variable named rotbuf_size which is the dimensions of a internal rotating buffer which is used to record the most recent samples in order to estimate the slope The sixth row sets a variable named delta_cnts this is the minimum number of counts that will be used to estimate a slope for a bright source it may use the most recent two samples but for a dimmer source it will go back through the buffer until it can find when the accumulated intensity was at least delta_cnts lower this is in order to have a good SNR for the slope estimations The seventh row set a variable named emit_predict_time which is how much in advance of the predicted threshold crossing time to start emitting exposure time updates 5 Software interface details still to be written needs at least three parts 1 description of how to connect to the expmsrv port and of the various types of data streams 2 description of commands sent to the expterm client 3 descriptions of expst commands update hv_on hv_off and of the returned status messages Also needs a description of format of the cnts file and of the fitinf
11. strument Description document http www ctio noao edu noao sites default files telescopes smarts tele15 chiron_0 pdf 6 Notes on Exposure Meter CHIRON software side The Chiron software connects to the Exposure Meter as yet another client It generates two connections one is for sending commands to the expm threshold request set for HV value and another to receive PM data used mainly to Real time graph for the observer On the other hand the exposure meter software connects to the torrent acquisition software panview to set the keywords that will be written to the fits header images The keywords are the ones explained section 4 of this document The figure below shows the general architecture and the Chiron Plug In that graphs the PM data For a complete documentation and details on this please refer to document CHI60S 2 6 Chiron software description and CHI60S 1 3 Chiron software User Manual E EXPOSURE METER PI_EXPMETER vi Front Panel SR File Edit View Project Operate Tools Window Help Exposure Meter Fits keywords cmds PM data O 1 1 600 600 Hiei Tabs alm
12. this should probably be fixed Here are their current contents expmeter expmeter EXPFITS4 more add_keys dbs set _queue_ em_timopn 0 STR dbs set _queue_ em_timcls 0 STR dbs set _queue_ em_numsmp 0 132 dbs set _queue_ em_avg 0 0 FLOAT dbs set _queue_ em_avgsq 0 0 FLOAT dbs set _queue_ em_prdsum 0 0 FLOAT dbs set _queue_ em_netint 0 0 FLOAT dbs set _queue_ em_mnwob 0 STR dbs set _queue_ em_mnwb 0 STR fits key add emtimopn dbs em_timopn shutter open time from exposure meter __ AFTER____IFNDEF__ 0000 00 00T00 00 00 000 fits key add emtimcls dbs em_timcls shutter close time from exposure meter _ _AFTER____IFNDEF__ 0000 00 00T00 00 00 000 fits key add emnumsmp dbs em_numsmp number of samples __ AFTER___ IFNDEF___0 fits key add emavg dbs em_avg average intensity _AFTER____IFNDEF__ 0 0 fits key add emavgsq dbs em_avgsq sum of squared intens _ AFTER _ IFNDEF__ 0 0 fits key add emprdsum dbs em_prdsum sum of products of intens and bin number __AFTER____IFNDEF __ 0 0 fits key add emnetint dbs em_netint net intensity after bckgrd subtraction _ _AFTER____IFNDEF__ 0 0 fits key add emmnwob dbs em_mnwob mean time without bckgrd subtraction __AFT ER____IFNDEF___ 0000 00 00T00 00 00 000 fits key add emmnwb dbs em_mnwb mean time with bckgrd subtraction _ AFTER__ __IFNDEF__ 0000 00 00T00 00 00 000 dbs flush em_timopn dbs flush em_timcls dbs flush em_numsmp dbs flush em_avg dbs flush
13. umulating the information needed to calculate the photon weighted mean time When the shutter close is detected the calculations are performed the information is written to the log and the info needed for the FITS headers are written to the appropriate output The expmsrv looks for client programs to connect to a particular socket Upon connecting each client sends an integer to indicate which one of several types of connections it wishes to make These mostly have the sense of being an output stream for expmsrv data There are two main clients which should probably always be running in normal production use of Chiron The first is the FITS client it requests the stream of FITS values As expmsrv calculates the exposure values and writes them to the log file and the fitinf file it also outputs them to all clients that asked for the FITS stream This client takes the stream and sends it to Chiron database system which is interrogated during the writing of the FITS header If the exposure meter has populated the database the values will appear if the system is down the FITS header values will be zeroes The second production client is called the early termination client It listens on a socket for target count values and receives a stream of integrated counts from the expmsrv If it has been sent a target count it will calculate for the current increase in counts when the target will be reached and send the Chiron control system a re
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