Comdyna Model GP-6 Analog Computer, Serial Number 794
Contents
1. further guess is that Comdyna originally assembled SN 794 with board 982 1 But then they might have discovered that board 982 1 was defective and retrofitted SN 794 with board 983 pre sale without removing board 982 1 Perhaps Comdyna just instructed the original purchaser not to use the multiplier network receptacles that are connected to board 982 1 Or perhaps Comdyna installed board 983 post sale when the original purchaser determined that the multipliers on board 982 1were defective and returned SN 794 to the Comdyna factory for repair under the warranty Just as for most used instrumentation the original paperwork for SN 794 including the specific user s manual instructions and any calibrations associated with SN 794 has long since disappeared2. is a response voltage It is appropriate for the analog computer programming that follows to rewrite the ODE in the form d i _ z u 2 o x o x Figure below is a somewhat general analog computer block diagram for solving this ODE provided that 0 lt lt 100 rad sec and 0 lt lt 0 05 These limits apply because the maximum standard input gain constant G for a GP 6 integrating amplifier is 100 Figure Author eBay User ID electrical_dynamics 27 January 2012 Comdyna Model GP 6 Analog Computer Serial Number 794 Two implementations of the circuit in Figure 1 are shown wired on the SN 794 patch panel in the photograph Figure 2 below Figure 2 The ODE solution shown on the screen of the digital oscilloscope in Figure 2 is the voltage output x of amplifier 6 that resulted from operating the particular circuit in Figure 3 below with only an initial condition x 3 50 V applied onto integrating amplifier 4 but no input u voltage The coefficient pots at the inputs to the integrating amplifiers shown in Figure 1 are not present in Figure 3 or alternatively you can think of them all as being set to the maximum value 1 Figure 3 The oscilloscope trace in Figure 2 is shown in greater detail in Figure 4 below Measurements on this record shows that the frequency of the signal is very close to the theoretically predicted value f 27 100 2z 15 9 Hz and the damping ratio also is ver
3. Author eBay User ID electrical_dynamics 27 January 2012 Comdyna Model GP 6 Analog Computer Serial Number 794 Comdyna Model GP 6 Analog Computer Serial Number 794 I Bare bones operating instructions These instructions are for the user who has knowledge of the basic functioning of an electronic differential analyzer more commonly known as analog computer for solving time dependent ordinary differential equations ODEs and would like to start using this GP 6 without having to slog through the Operator s and Maintenance Manual I ve used differential analyzers since the 1960s and Comdyna GP 6 and GP 10s since the mid 1980s yet I still can t decipher some of the details in that manual In accordance with the note on Figure 1 1 page 1 of the Operator s and Maintenance User Manual I placed a jumper across rear back plane terminals OP INPUT and OP OUTPUT for operating this GP 6 alone without any other GP 6s slaved to it Also I ve never figured out what the SW receptacles of the integrating amplifiers on the patch panel are supposed to do so I always place a jumper between the adjacent SW and OP receptacles Operator s and Maintenance Manual page 12 this works for my applications and I don t ask why Either before or after you apply power to the GP 6 you may wire up program your ODEs on the patch panel connect to the patch panel an external input instrument such as a function generator or switch
4. ave it alone I ll bet the switch can be repaired or replaced by a person with patience and circuit soldering skill Author eBay User ID electrical_dynamics 27 January 2012 Comdyna Model GP 6 Analog Computer Serial Number 794 3 If your ODEs are patched onto the patch panel you now may enter the coefficient potentiometer pot a variable resistor values Position the MODE SELECTOR rotary switch to POT SET and depress the IC mode control push button a Position the Y POT ADDRESS rotary switch to the number of the pot that you wish to set and the digital voltmeter display DVM will show the current value of that pot 0 lt value lt 1 b Rotate the knob dial of that pot CW or CCW until you set the value on the DVM that you want for the pot Repeat steps a and b for each pot that your ODE patching requires 4 When your ODEs are programmed on the patch panel and your coefficient values are all entered and your external input and display instruments are connected you may run the GP 6 to solve the time dependent ODEs With the IC mode control push button still depressed position the MODE SELECTOR rotary switch to OPR the ODE system is now in its initial condition IC a Next depress the OP mode control push button this actuates the electronic real time continuous analog as opposed to digital solution of your ODEs b To stop the solution for example when all dependent variables have reached steady state v
5. ctrical_dynamics 27 January 2012 Comdyna Model GP 6 Analog Computer Serial Number 794 IV Evaluation of the multiplier functions on SN 794 To test multiplier functioning I programmed each trio of multiplier network receptacles to multiply the outputs of the two separate circuits diagrammed on Figures 3 and 5 but with the circuits modified to eliminate damping feedback by removal of the 2 a G3 feedback connection shown on Figure 1 so that each circuit was nominally an undamped oscillator The SJ receptacle of a multiplier network must be connected to the SJ receptacle of a summing amplifier Operator s and Maintenance Manual page 13 I used the previously idle summing amplifier 5 for this so the product of the two oscillator signals was the output of summing amplifier 5 Contrary to what is printed on page 13 of the Operator s and Maintenance Manual the actual multiplier output signal is the negative product of the two input signals divided by 10 i e Eo A x B 10 not just Eo A x B Figure 6 is the digital oscilloscope screen image of signals from a run using the left side non standard multiplier network See the second paragraph of section II for the meaning of left side non standard Tek Age Acq Complete M Pos 400 0ms CURSOR Type Source at 636 0ms ze 1 572H2 aY 0 00V 3 Cursor 2 632ms ve 464 CHT 200V CH2 200V M 100ms CH2 7 4 804 CH3 1 004 27 Jan 12 08 31 lt 10Hz Fig
6. del GP 6 Analog Computer Serial Number 794 on the bottom edge Appearances can be deceptive though and only two of the apparent four multiplier networks function properly see section IV below All of the circuitry inside the blue case appears to be clean and functional Two of the original equipment small yellow precision capacitors apparently associated with integrating amplifiers 1 and 2 were replaced probably by a previous user with much larger silver capacitors I haven t detected any differences between the functioning of integrating amplifiers 1 and 2 and the functioning of integrating amplifiers 3 and 4 which apparently have all of the original precision capacitors But the replacement capacitors might be associated with time scaling which I did not test III Example solution of ODEs on SN 794 I show here an approach for solving by analog computing the standard 2 order vibration ODE from most basic linear systems and vibrations textbooks which is ae 2 2 X 260 X 0 X 0 U In this ODE u t is a time dependent input or forcing function time in seconds being the independent variable x t is the output function is the undamped natural frequency of vibration in radians sec and is the viscous damping ratio Possible initial conditions at time t 0 are x 0 x and x 0 x In the analog computer implementation here u t is a driving voltage say from a function generator or a switched battery and x t
7. ed battery and connect from the patch panel to an external display instrument such as an oscilloscope Be aware though that when you plug in or remove wires with power on the GP 6 is electrically live in particular the and 10 V receptacles are hot 1 Connect the GP 6 to 110 V AC electricity with a power cord plugged into the receptacle in the back plane of the blue case 2 Turn on the GP 6 by turning CW the COMPUTE TIME rotary switch dial on the operator panel until it clicks I don t turn that dial any farther CW because I don t know what else the COMPUTE TIME dial a variable resistor will do I run ODE solutions mainly in real time so I don t compress or expand the time scale which the GP 6 is apparently capable of doing The following steps 3 and 4 are with the X ADDRESS rotary switch on the operator panel in an unknown functional position This is supposed to be an 1 1 position switch but the lubricant on it has apparently dried up and hardened Consequently the switch is very difficult to rotate and the positions no longer click as they do on the Y POT ADDRESS and MODE SELECTOR rotary switches The X ADDRESS rotary switch position that I set unintentionally in the process of evaluating this GP 6 apparently does not interfere with any other standard functions of the GP 6 It is a sleeping dog that I decided not to rouse Unless you are prepared to repair the X ADDRESS rotary switch I recommend that you also le
8. oltage values 10 V lt value lt 10 V the overload limits assuming your ODEs are stable depress the IC mode control push button this re sets your ODE system to its initial condition Repeat the execution of the ODE solution as many times as you wish by depressing the IC and OP mode control push buttons II Condition of GP 6 Serial Number 794 This GP 6 appears to be in very good operating and cosmetic condition I have inspected it and played with its functioning for 3 4 hours I m not an electronics technician and I haven t tested all possible functions but I ve given it a pretty good workout The main thing I find that is not functioning as if SN 794 were new is the X ADDRESS rotary switch on the operator panel as described under paragraph I 2 above A standard GP 6 has two multiplier networks However SN 794 appears to have four with the patch panel receptacles of the non standard two positioned to the left and right of inverting amplifiers 7 and 8 at the bottom of the panel And there are two dual multiplier circuit boards one labeled 983 mounted on the backside of the patch panel the other labeled 982 1 mounted on the bottom surface inside the GP 6 blue case You can look inside the blue case and at the backside of the patch panel by loosening the two thumb screws near the top edge of the panel then rotating the panel forward about hinges Author eBay User ID electrical_dynamics 27 January 2012 Comdyna Mo
9. ure 6 In Figure 6 the output of summing amplifier 6 in Figure 3 the yellow signal was a 1 57 Hz 4 V peak to peak sinusoid the output of summing amplifier 7 in Figure 5 the cyan signal was a 15 7 Hz 5 V peak to peak sinusoid and the output of summing amplifier 5 functioning with the left side non standard multiplier network the purple signal was one tenth the negative product of the two sinusoids a modulated signal of maximum amplitude 2 V peak to peak I tested also the right side non standard multiplier network and it also functioned correctly However the two multiplier networks with receptacles in the standard positions on the patch panel just above summing amplifiers 7 and 8 did not function correctly For each when the SJ receptacle of the multiplier network was connected to the SJ receptacle of summing amplifier 5 the amplifier immediately overloaded The Author eBay User ID electrical_dynamics 27 January 2012 Comdyna Model GP 6 Analog Computer Serial Number 794 Operator s and Maintenance Manual page A11 recommends adjustments for 982 2 and 983 multiplier network circuit boards But I didn t take the time to fiddle with adjustments or conduct troubleshooting It is difficult to track visually the circuitry inside SN 794 but my guess no more than that is that the two functional multipliers are on board 983 and the two non functional multipliers are on the lower numbered and probably obsolete board 982 1 My
10. y close to the theoretically predicted value 0 05 Author eBay User ID electrical_dynamics 27 January 2012 Comdyna Model GP 6 Analog Computer Serial Number 794 Tek Anke Acq Complete M Pos 200 0ms CH2 Coupling BW Limit 100MH2 1 4 Voltage Invert i Off CH2 1 00 M 50 0ms CH2 1 88 24 Jan 12 16 07 lt 10Hz Figure 4 The analog computer block diagram of the other circuit on the patch panel in Figure 2 is shown in Figure 5 below This circuit is a factor of 10 slower than that in Figure 3 Figure 5 I tested this circuit also with an initial condition voltage applied to integrating amplifier 2 I measured the frequency of the response signal to be very close to the theoretically predicted value f 2m 10 2 1 59 Hz and the damping ratio also to be very close to the theoretically predicted value 0 05 In the process of testing this GP 6 I tried all eight amplifiers and all eight pots in the circuits of Figures 3 and 5 All of these components functioned nominally for this particular ODE solution Note on Figure 2 that summing amplifier 5 was unused in the circuits of Figures 3 and 5 shown in the photograph but even so a jumper connects the output of summing amplifier 5 to its input with a feedback resistor I ve found that such feedback is required on unused amplifiers just to prevent them from drifting into overload any time the GP 6 is powered Author eBay User ID ele
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