Hastings DV-20, Manual

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101B - PAGE 12
5.0 CALIBRATION AND TROUBLESHOOTING GUIDE
All Hastings Vacuum Gauges and Gauge Tubes have been carefully checked and calibrated at the factory before
shipment. If a calibration check is desired, the methods in the following sections may prove helpful.
5.1 Check Of Tube Accuracy:
The simplest and quickest method of checking operation and calibration of a gauge tube is to keep a new spare clean
gauge tube on hand as a "standard". To check operation, install both new and old gauge tubes together in the same clean, dry
vacuum system, and pump until a steady pressure is obtained. Plug the gauge onto both tubes alternately and check readings.
If the old tube reads a higher pressure than the new one, this indicates a calibration shift in the old tube which is most
probably the result of tube contamination. Calibration can possibly be restored by gently swishing the tube in a solvent such as
acetone, alcohol, or other non-polluting degreaser. After cleaning, thoroughly dry the tube and degas it before reinstallation in a
vacuum system to avoid system contamination by the solvent. If calibration cannot be restored by this procedure, replace the
old tube with a new gauge tube. The two tubes can track one another within close tolerance, however, the gauge calibration
can still be off. Check the gauge by methods described in Section 5.2.
5.2 Calibration:
5.2.1 Calibration Of All Models EXCEPT VT-4A, VT-5A, VT-5AB, & VT-6A
NOTE: If calibrating a cabinet model, remove top of case.
1) With power off and gauge tube disconnected, set meter mechanical zero to read on the center dot past "ATM" on the meter
scale for VT-4 models, and on the single dot past "ATM" for VT-6 models.
2) Turn on power and allow one hour warm-up for best results.
3) Install the gauge tube into a vacuum system as described in Section 3.5 and allow the tube to pump down to a
hard vacuum pressure (0.1 micron or lower).
4) Connect gauge tube cable onto evacuated new tube, or for quicker results, a compatible Hastings Reference Tube. The
vacuum gauge meter should now indicate approximately zero microns or the pressure marked on the reference tube; if such is
not the case, carefully adjust the CALIBRATION POTENTIOMETER (R-1) control to obtain the correct reading(s). (Looking from
the top of the meter, with the meter face towards you, the CALIBRATION pot access is to the left of the label.)
The instrument is now recalibrated.
5.2.2 Calibration Of Models VT-4A, VT-5A, VT-5AB, and VT-6A
The instruments listed above incorporate an amplifier to produce a voltage output and require four adjustments for a
complete recalibration. The alternate method will usually suffice for quick field checks as other adjustments, once
made, seldom require resetting.
NOTE: If calibrating a cabinet model, remove top of case.
1) With power off and gauge tube disconnected, set meter mechanical zero to single dot, or center dot, on right of
scale.
2) Turn power on, tube disconnected, and set OFFSET ADJUSTMENT (see Fig. 5.1) of amplifier marked "zero" to same dot as
mechanical zero. Allow one hour warm-up for best results.
3a) Pump gauge tube to hard vacuum (1 decade lower than first division on scale, i.e. pump DV-6 to .1 Hg or
lower). Connect voltmeter to output terminals. Set CAL ADJUSTMENT (see Fig. 5.1) for 1.00 volts DC.
3b) If meter scale does not read ZERO PRESSURE, remove the "DO NOT DISTURB" decal and set meter span to read ZERO
PRESSURE (see Fig. 5.1).
The instrument is now recalibrated.