902B Abs Piezo
Operation manual
19
Calibration and adjustment
The 902B is factory calibrated when delivered and in most applications further calibration is not required.
If the sensor element has been contaminated or damaged by process gases, adjustment of zero and full
scale can be executed to compensate for measurement errors.
Accuracy and repeatability
The 902B measuring accuracy is specified as transducer reading ± a percentage of the actual pressure. The
basic measuring accuracy is factory calibrated and cannot be user adjusted. The repeatability specification is
the transducers ability to repeat the same measurement value after multiple pressure cycles. Refer to the
transducer specification page 50 for actual values.
Gas calibration
The 902B Absolute Piezo sensor is gas independent and no gas calibration is required.
Piezo Zero Adjustment by serial interface
The Piezo zero adjustment can only be executed when the MicroPirani pressure measurement is below
0.1 Torr. The Piezo zero adjustment sets the Piezo zero reading.
Executing zero adjustment. (Evacuate the transducer to a pressure below 0.1 Torr)
Command:
@253ZER!;FF
Command values:
None
Command reply:
@253ACKZER;FF
Query:
@253ZER?;FF
Query reply:
@253ACK0;FF
Reset to default:
@253FD!ZER;FF
Factory default:
Factory adjustment value
Sensor value too high: @253NAK8;FF
The query feature reads the delta value between the user offset value and factory default value. This can be
used to monitor the positive and negative offset trend regardless of how many times the zero adjustment is
executed.
Zero Adjustment by use of the User switch
The transducer can also be adjusted by activating the user switch. When using the switch the transducer
must be evacuated to a pressure below 0.1 Torr. Press down the switch for 2 seconds and the LED will flash
green three times to acknowledge the zero adjustment has been executed successfully. The LED will flash
red three times if the adjustment has failed.
Piezo Atmospheric adjustment
The Piezo atmospheric adjustment allows the user to adjust the atmospheric reading for the Piezo
measurement.
Executing Piezo atmospheric adjustment. (Place the transducer in atmospheric pressure)
Command:
@253SPN!7.60E+2;FF
Command values:
Atmospheric pressure value
Command reply:
@253ACK;FF
Query:
@253SPN?;FF
Query reply:
@253ACK7.60E+2;FF
Reset to default:
@253FD!SPN;FF
Factory default:
Factory adjustment value
Sensor value too high: @253NAK8;FF
