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indy91
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« on: May 06, 2016, 08:44:00 AM »

The System Test Meter is now functional. It was a little bit tricky to exactly find out from where it gets the measurements and what exactly is displayed, but I think I have found a good first implementation.

As far as I can tell, the Signal Conditioning Equipment (SCE) is responsible for converting various AC and DC voltages and temperature measurements to a standard 0-5V range. The so scaled voltage are then given to the PCM TLM (Pulse-Code Modulation Telemetry) equipment, which converts the data inputs from the SCE and other data to a digital output. The System Test Meter seems to directly get its signals from the SCE output, so they are already scaled 0-5V.

In NASSP the SCE isn't simulated separately at the moment. In the simulation there isn't really much need to just have a separate class scaling voltages and such. So the scaling and conversion to the numbers the digital telemetry stream likes, are directly done in the PCM class. This implementation of the System Test meter directly draws its data from the PCM measurements. The telemetry data is all scaled 0-255, so there now is a System Test "Attenuator" which scales this back to 0-5V and selects the desired measurement depending on the two rotary switches. The attenuator also had to be wired to some kind of power source (without drawing power, it is always powered by the input voltage) so for now I have decided to wire it to the Flight Bus. In the future this should probably be wired to the SCE, but without power on the Flight Bus, there is no SCE power anyway.

The function of each System Test indication is not a constant throughout the Apollo program, so for now I have used the functions from the AOH:

-1A, 1B, 1C: Fuel Cell 1/2/3 N2 Regulator Pressure: I'm not sure we simulate this, so it will read zero for now. The measurement in the PCM is there, but it is set to zero.
-1D, 2A, 2B: Fuel Cell 1/2/3 O2 Regulator Pressure: Here there is a little error in the PCM class, because it uses the O2 tank pressure instead of the fuel cell regulator pressure. So for now this will read off-scale high from each function. I haven't immediately found, if the regulator pressure is measured somewhere, but maybe it could be calculated from the O2 flow into the fuel cell or something? I don't have the answer for this one.
-2C, 2D, 3A: Fuel Cell 1/2/3 H2 Regulator Pressure: Same issue as above.
-3B, 3C, 3D: Fuel Cell 1/2/3 Radiator Outlet Temperature: Correctly measured and displayed.
-4A: Battery Compartment Manifold Pressure: No idea, didn't find a measurement.
-4B: Battery Relay Bus Voltage: Correctly measured and displayed. Appears in some checklists (for later missions as 5B), so it is nice that this can be checked now.
-4C: Not Connected.
-4D: CSM to LM Current: Correctly measured and displayed, but not simulated yet, so always zero.
-5A: SPS Oxidizer Feedline Temperature: The simulation currently doesn't have separate propellant and oxidizer feed lines, so the pressures displayed on panel 3 and the feed line temperatures are identical right now. Also checked prelaunch.
-5B: Not Connected.
5C, 5D, 6A, 6B, 6C, 6D: CM RCS Injector Temperatures, I don't think this is currently simulated. Which means the CM RCS Heater switch is also not functional right now, if I saw it correctly. Sad
-The other functions are transponder stuff, not simulated yet I think.

« Last Edit: May 06, 2016, 09:12:12 AM by indy91 » Logged
kneecaps
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« Reply #1 on: May 07, 2016, 02:55:08 AM »

Great work! This is one of those meters that is easily overlooked but is very useful!
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"Okay. As soon as we find the Earth, we will do it."
- Frank Borman, Apollo 8

Current Work: ?? What next??

Future Work:
I know the AGC pretty well so anything need doing there?

On Hold/Completed:
SPS TVC in P40 issues.
P11 FDAI Error Needles (98%) complete. Comitted. Working A7 scenario.
P06 AGC Standby. Concluded. It's done by the AGC PSU.
Got us a complete AOH Volume II
macieksoft
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« Reply #2 on: January 11, 2018, 05:23:32 PM »

Quote
-4D: CSM to LM Current: Correctly measured and displayed, but not simulated yet, so always zero.

It is not displayed and is always zero, however it IS actually simulated now, i checked this and now i am sure.

My test procedure to check if CSM to LM current is simulated i performed:

In LM pull all CBs.
In CM close LM power cirtuit breakers and flip the switch to enable power from CM to LM.
In LM tie CDR bus to XLUNAR, then tie SE bus to CDR bus.
Push circuit breakers related with volt metter to monitor voltage and current on CDR bus.
Look at volt meter, should be showing about 28V for CDR bus and 0 for SE bus. Don't worry, this is normal when SE and CDR bus are tied and do NOT means that SE bus is not powered.
Now apply some current, push some CBs to get some current but not too much (about 15A gonna be perfect).
Back to CM check system test meter 4D, it will show 0 which certainly means it is not displayed correctly.
Now go to LM and start pushing all CBs. In some point current will rise enough to trip circuit breakers in CM, you will see volts and amps going to 0.
Go to CM and verify 2 LM power CBs are popped. They will be popped which means that CM to LM current is simulated (otherwise they wouldn't pop as they are triggered by CM to LM current).

Conclusion:
CM to LM current is simulated for sure, but the system test meter shows zero...

-4D: CSM to LM Current: Correctly measured and displayed, but not simulated yet, so always zero.
-4D: CSM to LM Current: Simulated and measured, but shows always zero which means it is not displayed correctly.
« Last Edit: January 11, 2018, 05:25:24 PM by macieksoft » Logged

indy91
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« Reply #3 on: January 12, 2018, 06:39:00 AM »


Conclusion:
CM to LM current is simulated for sure, but the system test meter shows zero...

-4D: CSM to LM Current: Correctly measured and displayed, but not simulated yet, so always zero.
-4D: CSM to LM Current: Simulated and measured, but shows always zero which means it is not displayed correctly.

Yep, you are right. I think I just didn't know at the time that we already simulated this. If I find the right electrical device to ask the current from (could be Saturn::LMUmbilicalFeeder) then this can easily be added to the System Test Meter measurements.

EDIT: This has been added now. I get about 2 Amps normally. But I am also getting this weird bug where during the first connection of CSM power to the LM a seemingly random wattage is attempted to be drawn and that exceeds the max ampere rating of the LM power circuit breakers in the CSM. So the two CBs are plopping open. When I push them in again everything seems fine. Are you getting that as well @macieksoft?
« Last Edit: January 12, 2018, 07:50:57 AM by indy91 » Logged
macieksoft
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« Reply #4 on: January 12, 2018, 10:34:13 AM »

I diid following:

Docked to LM and extracted it from stage.
Switch to LM and pull all CBs.
Go to CM and make sure LM power CBs are pushed (they were) and then i switched the lm power switch to on. CBs didn't popped.
Now back to LM, i tied CDR bus to XLUNAR and then pushed DC volts CB to enable voltmeter, voltmeter shown 0V for CDR bus.
Then i switched to CM and fount that CBs were popped.
I switched the switch to reset then to off, pushed CBs and switched switch to reset and then to ON. CBs didn't popped.
Back to LM and i found that CDR bus volt meter was showing 28V (thats fine).
Now i pushed some CBs to get a little current. LM amp meter needle bearly moved, i bet i got about 2A or so.
Go to CM, CBs were pushed (thats fine) and i checked 4D, system test meter needle was between 1 and 2.
Now in LM i pulled some of the CBs to decrease load. Now LM ampmeter was preatty much at 0, just a very little current flowing.
In CB i checked system test meter needle that was showing about 1 (notable decrease which was fine).

Conclusion.
-CBs appears to pop when i powered CDR bus from XLUNAR for the first time, or maybe when i powered volt meter from a CDR bus tied to XLUNAR for the first time.
Then after resetting switch in CM and CBs in CM all worked fine without popping CBs.
-System test meter is showing the current and reacts to the current changes.
-System test meter appears to be scaled 1V per 1A of current flowing or so. It is suspicious to me because the max reading in this case would be just 5A which is very small.
-CBs appears to pop at about 20A (i don't know exact value, may be even less than 20A) which is also quite small, not even sure if i could power IMU and AGC without making them pop.
About 20A is the result of previous testing, they seems to pop before ampmeter reaches 20A.

Questions:
What available documentation says about scaling of system test meter for this measurament?
What available documentation says about current which should trip both CBs in CM when both CBs are pushed?
« Last Edit: January 12, 2018, 10:38:24 AM by macieksoft » Logged

indy91
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« Reply #5 on: January 12, 2018, 10:48:02 AM »


Conclusion.
-CBs appears to pop when i powered CDR bus from XLUNAR for the first time, or maybe when i powered volt meter from a CDR bus tied to XLUNAR for the first time.
Then after resetting switch in CM and CBs in CM all worked fine without popping CBs.

Yeah, I was getting the same behavior here. I had amps as high as 9500A (checked that in a debug string), but it was pretty random. So I think some variable isn't initialized right. I'll look through our code on the CSM side and LM side for this.

Quote
-System test meter appears to be scaled 1V per 1A of current flowing or so. It is suspicious to me because the max reading in this case would be just 5A which is very small.

What available documentation says about scaling of system test meter for this measurament?

The scaling is from 0 to 10A to 0 to 5V. That is according to the available documentation (https://history.nasa.gov/afj/ap15fj/csmsc/1-28.gif) and what we are using. That's why the usual value is 1V, indicating 2A.

Quote
-CBs appears to pop at about 20A (i don't know exact value, may be even less than 20A) which is also quite small, not even sure if i could power IMU and AGC without making them pop.
About 20A is the result of previous testing, they seems to pop before ampmeter reaches 20A.

What available documentation says about current which should trip both CBs in CM when both CBs are pushed?

Both circuit breakers for the LM power are having a max amps rating of 7.5A. So you can draw 15A before the CBs are going to pop. It's really only meant to power the standby heaters in the LM, not anything like the IMU or AGC.
« Last Edit: January 12, 2018, 10:51:26 AM by indy91 » Logged
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