PCM-STD-40M and PCM-STD-100M Test and Supply Pressure Sensor Coefficients
The Pressure Control Module's (PCM) Test and Supply pressure sensors must indicate close to atmospheric pressure when the ports are open to atmosphere. If the Test Sensor is far from atmosphere then the PCM will not open the Pressure Measurement Module's (PMM) isolation valve. This can show itself as an inability to complete a vent process, a controller 500 error, and the active module selection remains on the PCM. The cause is due to the sensor not correctly zeroing. It is a known problem with PCM firmware 1.02 and 8270A/8370A system firmware 1.00. The current firmware versions automatically adjust these sensors. See this article to update the firmware, 8270A / 8370A firmware update instructions
The solution is to manually update the sensor's C0 offset coefficient. If the Test Port sensor has drifted, then the Supply Port sensor may have also drifted. A direct remote interface tool is required to query and write commands to the 8270A/8370A. The C0 unit of measure is “kPa”.
Continue reading below the images for the procedure to adjust the coefficients.
The 8270A/8270A serial interface defaults to 9600,N,8,1 and if you're using a the 9-pin RS232 port then a NULL MODEM cable is required. if you use the USB port it will map to Windows as a virtual COM port.
Use the following commands to adjust the Test and Supply sensor offset coefficients. The Test and Supply ports on the 8270A/8370A should be open to atmosphere.
Test Pressure Sensor
CAL:PRES4:DATA:VAL1? -- Command to read the current test pressure sensor C0 offset value.
CAL:PRES4:DATA:VAL1 xxx -- Command to write a new test pressure sensor C0 offset value where xxx is a numeric value in kPa. Based on the example picture, start with "250" and see how the Test Port pressure measurement responds. Continue to update the offset until the Test Port sensor indicates approximately 14.7 psia
Supply Pressure Sensor
CAL:PRES6:DATA:VAL1? -- Command to the current supply pressure C0 offset value.
CAL:PRES6:DATA:VAL1 xxx -- Command to write a new pressure sensor C0 offset value xxx is a numeric value in kPa. Based on the example picture, start with "290" and see how the Supply Port pressure measurement responds. Continue to update the offset until the Supply Port sensor indicates approximately 14.7 psia
No save command is required – new coefficients are automatically saved upon write. The C0 values are in units of kPa.