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Tool/software:
Hello,
I am looking for help verifying connections for the "one wire" calibration method. For the attached circuit (figure 6-3 of PGA308 manual), I don't see any explicit guidance in the manuals and would like to verify the following hardware connections/settings for writing calibration gains to the PGA308.
T4 (Vout_F) to "one wire or Riso of circuit.
T4 (ground) to Iret of circuit.
T1 (Vref Ext) to 4-20 high of circuit.
T1 (Ground) to 4-20 low of circuit.
Ryan,
I am working on a comprehensive answer to your question. I will get back with you tomorrow.
Art
Ryan,
Attached is a step-by-step guide on how to calibrate using the PGA308EVM. This calibration procedure makes use of the built-in sensor emulator. You will need a +/-15V supply, a floating 12V supply, and a 9V supply. Once you have done the calibration with the sensor emulator successfully, I can help you with your real-world sensor and/or your sensor module.
I hope this helps.
Art
Art,
This is very thorough and helpful. We really appreciate the help. This looks like a great guide for this specific case. I'll run the emulator calibration and will be following up for guidance on calibrating my real world sensor module.
Best,
Ryan
Art,
I made it through page 12 steps and get an error message "Zero DAC is out of range: -2.5<Fine_Gain<2.5" and sometimes "Fine Gain Out of Range: Fine Gain Range: 0.33333<Fine_Gain<1.0000"
I am connected identical to pages 5 and 6 with the exception of the 9V supply and 12V floating supply using different outputs of the same power supply. The floating supply and INA power are isolated to separate power supplies. I noticed your bottom meter on page 6 is reading 14V. Is the target +-12V here?
I double checked all of the jumper settings.
I'm running approx. 15mA on the ammeter during cal and approx 25mA after cal.
Any suggestions? Thanks for the help!
-Ryan
Ryan,
best regards,
Art
Art,
Thank you for looking into this, we certainly appreciate it. I'll isolate the 9V and 12V supply as well as do all of the recommended settings and jumper checks. Hopefully we find something obvious! I won't be back in the lab until tomorrow but will follow up ASAP. It's encouraging to know we can do a call if we need to.
-Ryan
Art,
Great news, we ran a successful 4-20 cal on the internal chip and are ready to write to our external chip. I isolated the 12V and 9V with no change. It turned out to be that my +14 and -14 source ground termination was incorrect.
Our external circuit is identical to figure 6-3 above. Can you assist with similar guidance for writing calibration gains to that chip?
Best,
Ryan
Ryan,
I think you want to connect your own sensor module and program that module ( as us shown in the image below). This document shows how to do that: Connections to custom sensor module
I hope this information helps! Best regards, Art
Art,
Thank you, this certainly helps! We're just about done in the lab for the week and will give Option 2 a go when we pick up next week.
This looks pretty straight forward for the most part. I assume there are software settings I'll need to adjust. Specifically the one wire control within the load preset tab? (image below)
Ryan,
I'm glad you are making progress. Best regards, Art
Art,
We really appreciate the detailed and thorough help!
I'll give this a go later this week when I'm back in the lab and follow up.
Best,
Ryan
Art,
Okay so not quite there but made more progress. Getting the error message "Fine Gain Out of Range: Fine Gain Range: 0.33333<Fine_Gain<1.0000" after applying upper limit to sensor (full bridge load cell). Can you help verify my variable (4) below and look for any other suggestions? Thank you!
Sensor module connections: connected my sensor module (containing XTR116, PGA308, and other components identical to figure 6-3 above), using page 11 connections to J3
Sensor connections: double checked and wired via module output diagram
DAQ power connections: double checked and wired via page 10 connections
DAQ jumper settings: double checked and wired via page 5 settings (same as internal settings from before)
Variables I'm looking into:
(1) My sensor bridge resistance/span/gain are within PGA308 tolerable ranges. Currently using a small puck style 250lbf full bridge load cell with a nominal gain of 2.0+-1% mV/V, an input impedance of 750ohm, and an output impedance of 700ohm.
(2) Ensuring exact application of load to puck. Was using weights in the lab which were only approximately 2/3 of sensor capacity but consistent. I assume this is okay for a proof of concept, giving an inaccurate mA/lbf output, but okay for just initial go-no go system checks. I did run a cal with the sensor disconnected and received the "Zero DAC is out of range: -2.5<Fine_Gain<2.5" so I know the sensor is being seen by the 308. I did make it through cal at one point to the second low point step and then errored out on that step. The DAQ measures the upper limit @ 18.76mA and lower limit @ 18.77mA which doesn't make sense.
(3) Verify sensor module board traces and pinouts/footprints match figure 6-3. I've double checked these but will check again. The sensor excitation is correct and 4-20 loop is running in the right ballpark.
(4) Verify the XTR Scaling tab within the load presets tab does or does not need to match sensor module circuit. I changed these component values from default to match the sensor module circuit with no change either way. Images below.
Default Settings:
Modified Settings To Match 6-3 sensor module:
Error message and outputs:
Ryan,
Thanks for the excellent notes. I hope we can resolve your issue quickly.
I hope this helps! Best regards, Art
Art,
Thank you! This is becoming quite the long support thread for you and we really appreciate the help. I won't have time back in the lab until Monday but will start following up on these now for a placeholder. I ran through all of the PCB traces, datasheet pinouts, and component placements with no problems found.
1: Sensor offset is listed as <1% of rated output (~8mV like you mentioned) so calculation yields a very low 0.08mV. Will follow up and measure this in the lab.
2: Will follow up and measure this in the lab.
3a: Vexc was running right at ~4.096V (measured), and didn't get a voltage across Sense+ and Sense- which I guess would mean offset is low. Will follow up and measure this in the lab and verify Vexc at the actual 308 (pin 10 Vref) as well as grab 308 output voltage from 308 (pin 9 Vout).
3b: I measured/configured these both ways with same error but will certainly not lose sight of this as calibration develops.
3c: Original results on the ammeter yielded strange values; sometimes would drop to ~7mA for both low and high cal points and then ~18mA for both high and low on other runs...couldn't make sense of it. Will follow up and measure this with actual values.
3d: Will follow up and measure these in the lab. I would be mostly curios about Vout as well...
4: Great idea with using the EVM board as troubleshooting logic! I'll give this a go if all else fails above.
Thanks again and I'll plan on following up Monday.
Best,
Ryan
Ryan,
I provide one short response, and wait for you to do further measurements:
The way the calibration algorithm works is that it initially sets all the gain values to minimum gain, and all the offset values to try and force the PGA output to mid scale. Thus, if the PGA309 input was 0mV the output would go to 12mA (mid scale for a 4mA to 20mA transmitter). On the other hand, if the input is 1mV, the output will move to something like 12.5mA. In both cases the calibration algorithm can then calculate the input voltages based on the output, gain, and offset settings. Once the PGA309 input is known for minimum and maximum pressure (strain or whatever stimulus), the gain and offset can be adjusted to achieve the desired output range (4mA to 20mA). The key point here is that you should expect to see outputs in the 12mA range at first while the algorithm determines the input. Below is the algorithm math details.
PGA308_calibration_procedure.pdf
Best regards, Art
Art,
Thank you, this logic will help me run through diagnostic measurements as I'm debugging.
I'll be back in the lab tomorrow and will hopefully be responding back with something definitive!
Best,
Ryan
Art,
Okay so I made some progress but still fail with same "Fine Gain Out of Range: Fine Gain Range: 0.33333<Fine_Gain<1.0000".
Responses to measurements/questions:
1: Sensor offset is 8mV. measured zero scale = 0mv full scale = 8mV
3a: raw Vexc @ pin 10 on the 308 is 4.086 which matches sensor Vexc at connector.
3b: image below, adjusted to external module circuit.
3c: amperage (I didn't get good results here and may need to reconfigure my meter, levels fluctuated around 1-1.5mA which doesn't make sense)
3d: (value = zero scale-full scale): (Vin1 = 2.044-2.048), (Vin2 = 2.044-2.040), (Vs = 4.853-4.853), (Vref = 4.086-4.086), (Vout = 0-3.990)
4: Sensor "passes" calibration using EVM board but automatically switches the output mode to Vout. (image below). Is it possible that I'm missing a software setting somewhere for scaling to my sensor module instead of EVM? Images below
Ryan,
On Oct 11, you mentioned "Great news, we ran a successful 4-20 cal on the internal chip and are ready to write to our external chip.". I think used an older version of the PDF below to do the setup. I ran through this again today and added a few slides, so the updated file is given below. The update was to add a few slides about programing OTP. When I ran through this procedure, the software did not switch back to Vout mode when I finished. Even after closing the software and opening it again it retained current mode. When I did my calibration I set the sensor emulator to output 0mV and 8mV. When I completed the procedure I programed OTP, cycled power, shut down software, and restarted the software. After the restart, I was able to get 4mA to 20mA with 0mV to 8mV input. The last slide in the presentation shows the gain and offset values that the PGA308 was set to for your input signals.
I notice that you have "load post cal" check-box checked. I think this may be the issue. The purpose of this feature is to select a post-cal configuration that enables features that should be turned-off during calibration. For example, during calibration you do not want over-scale or under-scale enabled, because that may limit your output range which could impact calibration results. This feature can be enabled after the gain and offset values are determined using the "load post cal" check box. In your screen-shot you don't have a file selected for post cal. I think it is likely that a voltage output mode post cal is being selected and that is what is causing the issue.
Can you repeat the basic calibration outlined in the PDF below with the "Load post cal" checkbox unchecked? When you do this you can set the sensor outputs to 0mV and 8mV (in the location marked Step 5b). When you step through this you should get very good post calibration accuracy. Also, you should not see the calibration mode switch to Vout mode (it should stay in current loop mode). You could program the OTP and you should see that the values retain after cycling power. If you get all the expected results, then you can go back to your external sensor. If you get the out of range message in this case, than you have a sensor issue or a wiring issue. You should use a volt-meter to verify the input signal if you don't get the expected results.
Sorry for the difficulties you are having. I hope we can resolve them quickly.
Best regards, Art
Art,
Thank you, I really appreciate the detailed help. This is encouraging! I was really hoping it could be software related as I've triple checked the PCB, components, and wiring.
One question: Do I configure the block diagram settings to the same settings shown on page 7?
I'll be back in the lab in the morning and will run through these scenarios. I loop back with my results.
Best,
Ryan
Ryan,
You should not have to configure the block diagram at all. The pre-cal file and calibration process will do all the configuration. The block diagram is really most useful as a way to see what the calibration process did. Technically, you could select "Run out of RAM" mode in the lower left corner and then you could manually adjust the different gains and offsets for the PGA308. I really never do that thought, as I generally let the calibration choose the values for me.
Best regards, Art
Art,
Thank you, I ran again this morning with mixed results.
Excluding the load post cal feature I was able to calibrate and measure post cal results successfully and accurately with the EVM board connected to my load cell, and not revert to Vout settings. So we're good to go there as far as software settings go there.
Unfortunately when connecting the external 4-20 board configured identical to figure 6-3 on page 78 of the PGA308 manual we still fail with the same fine gain error. Something is going on with my current loop. Measurements of the EVM vs external 4-20 are as follow. Voltages look nearly identical, while the current is not. I think at this point I'm leaning towards my XTR being damaged/faulty or capacitors being misplaced. I'm going to layup another board with new components to rule this out.
I'll loop back with results once I layup a new board and test.
Thanks again for the help! Hopefully this will be the missing link.
Art,
No luck with swapping components. Swapped the XTR116, capacitors, and BJT with new and correct value components and have the same results as listed in the table above. A few questions listed below.
1: Is it possible the PGA chip is damaged and still has the correct voltage outputs above? I'm going to start laying up an entire new board to verify that.
2: Are there specific jumper settings on the DAQ that need to be changed when switching from the EVM board to the external 4-20 module?
3: Are there specific software settings that need to change when switching from the EVM board to the external 4-20 module?
The calibration passes when sensor is connected through the EVM board but fails with fine gain error when the EVM is replaced with the external 4-20 module.
Best,
Ryan
Ryan,
7140.pga309-USB-DAQ-connectipon-to-custom-sensor-module.pdf
best regards, Art
Ryan,
If you like, send me an E2E friend request so that we can switch to email, and set up a meeting. I think a call might be the quickest way to debug this issue.
Best regards, Art
Art,
Okay great, I appreciate it! A call might be best. I sent a friend request and I can put together the responses to your last thread realistically on Monday when I'm back in the lab.
-Ryan
Ryan,
I just sent you and email. Please let me know when you want to set up a call. Let's close out this E2E thread. We can move to direct email and phone calls. I really thing you are very close to getting this to work and the call should take care of the last few details.
Art