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149-072011 Model 2002 Vacuum Gauge Page 11 of 38
An important point to be noted is the fact that after the adjustment, the new calibration coefficient is only in
temporary memory. If the instrument were unplugged at this point, it would revert back to the original
displayed value upon restarting. Place the Model 2002 back in the RUN mode to store all of the current
calibration coefficients in permanent memory.
To perform a full calibration on the Model 2002 system, first use the Zero Coefficient Adjustment
Procedure. Followed by the Midrange Coefficient Adjustment Procedure, and finally perform the
Atmosphere Coefficient Adjustment Procedure.
Zero Coefficient Adjustment
The zero coefficients corrects for the constant power level which is present over the entire pressure range.
Typically, this adjustment corrects for low pressure errors. The instrument will need to be re-zeroed often if
measurements are being made in the 10-4 Torr range, especially if the ambient temperature changes. The
transducer may have a temperature coefficient of up to 2x10-4 Torr/oC. The instrument remote zero input
will allow an external gauge such as an ion gauge to automatically re-zero the Model 2002 whenever the
pressure drops below the desired pressure level (if it has a TTL output).
NOTE: Do not attempt to zero the Model 2002 in pressures above 10-2 Torr; the microprocessor will not accept a
zero above this pressure.
To manually adjust the zero uses the following procedure:
1. If possible, evacuate the vacuum system into the low 10-6 Torr (1.33x10-6 mbar) range or as low as possible
below 10-4 Torr.
2. Allow the sensor to operate in this condition for a minimum of 15 minutes.