Teledyne HASTINGS 2002, Instruction Manual, Page: 12 / 49

page 12
Maintainance and Repair 4-3
Zero Coefficient Adjustment
The zero coefficient 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 1x10
-4
Torr/
o
C.
The instrument remote zero input will allow an external gauge such as an ion gauge to automati-
cally 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 micro-
processor will not accept a zero above this pressure.
To manually adjust the zero use 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.
3. Place the instrument in the CAL mode, then simultaneously press the UP and DOWN arrow
keys. The CAL light will start to flash indicating that the calibration mode has been activated.
4. Press the zero button once if below 6x10
-5
Torr otherwise use the up and down arrows to adjust
the display of the Model 2002 to match the pressure indicated by the reference. If using the
up and down arrows to adjust the display, wait 20 seconds between presses to allow the
adjustment to take affect.
5. The unit is now fully zeroed. Place the Model 2002 back in the RUN mode to store the zero in
permanent memory.
Midrange Coefficient Adjustment
The midrange coefficient corrects for errors in the slope of the power curve. Typically this is due
to the geometry of a particular sensor and will only need to be performed once in the lifetime of
the sensor. This adjustment might be needed if a full calibration is being performed in a gas other than
nitrogen. The zero adjustment will need to be performed before making this adjustment .
To adjust the midrange coefficient use the following procedure:
1. Evacuate the vacuum chamber and refill with the desired gas to a pressure of 7 Torr, as
indicated by a reference vacuum gauge.
2. Press the mode switch repeatedly until the CAL mode is illuminated.
3. Simultaneously, press both the up and down arrow keys. The CAL light will start to flash,
signalling that the calibration can now be conducted.
4. Press, hold and release the up and down arrow keys as necessary to adjust the display to match
the pressure indicated by the reference. Note: It may be necessary to hold the desired key
down for 5-10 seconds before any movement is seen.
5. Press and release the mode key as necessary to return the 2002 to the RUN mode and store
the coefficients to permanent memory.