pg. 20
MicroPirani Zero Adjustment by serial interface
The zero adjustment function changes the MicroPirani measurement offset at low pressure. Temporary or
permanent shift in zero offset can be caused by contamination, corrosion, electrical noise interference and
temperature.
Zero adjustment only changes the low measuring range and will have no influence on
measuring errors in the range from 1×10
-2
and above.
If the transducer is reading 8.00E-5 Torr at an actual pressure of 1.00E-5 Torr, the offset error is +7.00E-5 or
700% error of actual pressure. At two decades higher pressure of 1.00E-3 Torr the offset error is a factor 100
lower when measured of the actual value, so the 7.00E-5 Torr offset will cause a 7% error at 1.00E-3 Torr.
To obtain best measuring performance, the transducer should be evacuated to a
pressure below 8×10
-6
Torr before executing zero adjustment.
Zero adjustment can be executed at higher pressures, but this can cause inaccurate
reading below the zero adjustment value.
Executing zero adjustment. (Evacuate the transducer to a pressure below 8×10
-6
Torr)
Command:
@253VAC!5.00E-5;FF
Command values:
None, 1.00E-5 to 5.00E-3
Command reply:
@253ACK;FF
Query:
@253VAC?;FF
Query reply:
@253ACK5E-5;FF
Reset to default:
@253FD!VAC;FF
Factory default:
Factory adjustment value
Sensor value too high: @253NAK8;FF
After execution of zero adjustment the PR1 reading will be 1×10
-5
Torr. If the pressure measured by the
transducer is higher than approximately 1×10
-2
Torr then the zero adjustment cannot be executed. This
indicates that the transducer is contaminated and should be serviced. See page 52 for Service and
Maintenance procedures.
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.
Piezo zero adjustment
The Piezo zero is automatically zero adjusted when the MicroPirani measurement is below 5×10
-2
Torr and
consequently under normal operation it’s not necessary to perform user adjustments. The Piezo zero
adjustment can only be executed when the MicroPirani pressure measurement is below 1×10
-1
Torr.
The Piezo zero adjustment sets the Piezo zero reading.
Executing Piezo absolute output adjustment. (Evacuate the transducer to a pressure below 5×10
-2
Torr)
Command:
@253ZER!;FF
Command values:
None
Command reply:
@253ACK;FF
Reset to default:
@253FD!ZER;FF
Factory default:
Factory adjustment value
Sensor value to high: @253NAK8;FF
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 8×10
-6
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.
MicroPirani Atmospheric adjustment
The MicroPirani atmospheric adjustment allows the user to adjust the MicroPirani full scale reading. Vent the
transducer to atmospheric pressure using the gas that corresponds to the gas calibration setup. Atmospheric
adjustment can only be executed with air or Nitrogen.
