XTR108EVM-USB Manual Calibration

Hello Kuramochi-san,

If the output current doesn't change it indicates that the input resistance is not changing when the button is pressed. Can you have the customer measure the resistance of the RTD input for both the "Set RTD Emulator to Minimum Scale" and "Set RTD Emulator to Maximum Scale"?  This will help us understand if there is some malfunction with the EVM that is preventing the relays from switching the resistances properly.

Hello Ian,

I am having a similar problem using the XTR108EVM-USB.  Using the default resistors and Model_files\4-20mA, CH! 0-300C.csv I am able to load the model file, calculate initial settings, set the pots to the correct values and proceed to First Corrections box.  Selecting the "Set RTD Emulator to Minimum Scale" shows a value of 3.945mA.  Selecting the "Set RTD Emulator to Maximum Scale" does change the lit led to D7 (RTD max) but the reading remains the same (3.945).  Measuring the inputs V/I-0 and V/I-1, it appears I have no current flowing and no mV signal.  Taking it a step further I can measure resistance, I know it's not a good practice but I'm desperate, at the inputs of 200 ohms at zero and about 312 ohms when the rtd emulator is set to max scale in First Corrections box so I believe the signals should be getting there.  I do have 5V on the Vs pin.  I have replaced the xtr108 and verified the "find resistors" values a couple times with no success.  I also uninstalled and reinstalled the software.  The end goal is to use the interface to setup our own sensor board and a PT1000 RTD, without having to calibrate the actual PT1000 rtd's in a production environment.

Thanks in advance!

Regards Bill

Hello Bill,

Have you double-checked that the resistor values given after entering in your operating conditions and pressing "Calculate Resistors" match the resistor values on the PCB? Sometimes the input common-mode voltage range can be violated with an improper Rcm value.

Do your jumper settings match the default settings given in Table 19 of the XTR108EVM-USB user's guide?

Since you are trying to test current output mode, are you applying a 12V to 24V DC power supply to J4 on the Interface PCB?

Best regards,

Ian Williams

Hi Ian,

Thanks for the quick response. I believe it was a bad solder joint on Rcm. It threw me off because the registers were at zero for the current output and I was able to change them and get it to respond. I was able to attach our "CE front end" to the circuit, change the emulator pots and calibrate a PT1000 perfectly. I had one question on the unused op amp. The plus input is grounded on the eval board which isn't always good on single supply systems with discreet op amps.. Would this be ok to do for my design or would it be better tied to the ref which is also unused.

Thanks again,
Bill

Hi Bill,

I'm glad you found the problem on the board. 

Regarding the unused op amp, all of its input/output pins are grounded through 0-ohm resistors R6, R7, and R8 as per the schematic on p.49 of the XTR108EVM-USB User's Guide. If you remove those resistors, you can make other connections to the op amp with the OPAout, OPA In-, and OPA In+ test points or the solder pads of the removed resistors.

I don't see a problem with grounding all the pins on the op amp. Even in current output mode, the onboard FET regulates the loop supply voltage down to about 5V, just like in a typical single-supply system. 

Best regards,

Ian Williams

Hi again Bill,

I just encountered a similar quirk while using the EVM. It turns out that I didn't have loop power applied to the system before starting the software, so the initial EEPROM/register reads returned erroneous values. This prevented the input MUX and input current source assignments from happening. If you see a similar problem again, make sure you have power applied, and check the input MUX and current source assignments in the Block Diagram tab.

Best regards,

Ian Williams

Hello again Ian,

 

I have made my own board for the xtr108 and am having a couple issues.  The EEPROM 25C040 seems to be the only EEPROM I can get to work on the evm sensor board.  Maxim has a "not recommended for new designs" note on the data sheet and had a substitute but it doesn't work.  I ordered several other 4K SPI EEPROM's and haven't been able to get any to work.  They set all the mux to all 5's. On the XTR108 board that I made, I am having a issue with step 2 "set rtd emulator".  I am reading high resistance numbers and drawing excess current when hooked up to my board.  If I skip this step and assume the rtd values are set I can trim the unit fine at the next steps.  Seems like I have a ground loop during the resistance measurement.

 

Thanks in advance for your help.

 

Bill

Hello Bill,

Microchip recommends the 25LC040A as a replacement, which seems to be equivalent other than being offered in a different package and having slightly lower minimum supply voltage and faster maximum clock frequency. It's in production with no signs of obsolescence. Have you tried this device?

Are you using your own PCB for the XTR108 but the Interface PCB and USB-DAQ PCB from the EVM? If so, you should just need to follow the schematic design as done in the XTR108EVM-USB, as I've attached below. The software should handle all the appropriate relay switching on the Interface PCB such that only one measurement (R, V, or I) is happening at any given time. Also make sure that you're using a 4-wire connection to the DMM for resistance measurement.

XTR108_Sensor.pdf

Best regards,

Ian Williams

Hi Ian,
Today I received 50 pcs. of the 25C040 EEPROM that comes on the evm board. I put that on the evm board and even that one doesn't work. I had a second brand new developement kit and pulled the eeprom off and it works perfectly on the other one. I tried putting a new eeprom on the brand new evm board with no luck. It seems to set the mux and registers to wrong values. So far the only two eeproms that work came from the dev kits.
Yes, the board I built is connected to the daq interface. I have the 34401A meter and GPIB-USB-B. I was able to set up my board skipping that resistance measurement step (and using the EEPROM from off one of the EVM sensor boards.) I copied the circuit exactly but added a CE "front end" which may have created a ground loop when the resistance measurement is selected.

Hello Bill,

I think the issue may be related to the checksum of the EEPROM not being written correctly, therefore preventing communication. Try installing a fresh 25C040 on your board and running this test procedure software which is used during assembly of all new XTR108EVMs.

Download the software here.

Best regards,

Ian Williams

Hi Ian,

I am in the process of restarting this project and the link for the test software you provided doesn't work.  Has this issue been fixed with a software update or will I still need this software? 

Thanks in advance,

Bill

Hi Bill,

The link expires after one week. Here's an updated one: txn.box.com/.../0qoo7khndsax8gxqs63oxozm0f1chqpr

Best,
Ian Williams