Teledyne DNV-33D 4.2DNV-33Calibration, 4.2.1Reference Check, 4.2.3Optimizing Gauge Tube Accuracy

4.2DNV-33 Calibration

All calibration voltages are factory set and will rarely change. The methods for checking gauge calibration are detailed below:

4.2.1Reference Check

The DNV-33D incorporates a quick reference check reading. To utilize this feature the front panel switch must be in the TEST position. In this position the digital display should read “400” (+3). If it does not read this the calibration GAIN pot should be adjusted to bring the reading back to “400”. This will bring the gauge back on the standard average calibration curve. NOTE: The signal output will change when the switch is put in this position and the set points may trip.

Pump the gauge tube down to hard vacuum. Set the front panel switch to the ‘CAL’ position. Adjust the ‘CAL’ pot in the rear of the unit for 000 on the display. If there is a midscale refer- ence available to the system, see section 4.2.3 on recalibration. Calibration is complete for use with the standard average curve.

4.2.2Recalibration for Different Length Gauge Tube Cables

A maximum of 100 feet of gauge tube cable can be utilized by the DNV-33D. If the cable length or size (18 gauge) is changed, the unit must be recalibrated. The procedure for recalibration is described in section 4.2.1.

4.2.3Optimizing Gauge Tube Accuracy

Individual tubes can be trimmed for best fit upscale on the curve by performing a calibration adjustment of the gain pot vs. tube output against an accurate reference standard, to do this:

Pump the gauge tube down to hard vacuum. Set the front panel switch to the “CAL” position. Adjust the “CAL” potentiometer in the rear of the unit until the display reads 000.

Pump the system to a known pressure using a reference in the system. At this pressure, adjust the gain potentiometer until the display reading matches the reference reading. The unit should now be calibrated. Best average fit to the curve will occur if 700 mTorr is used for this setting. Do not use this instrument with another tube unless resetting the gain to “400” per 4.2.1 or performing the above procedure for the specific tube.

5.0Notes on Vacuum Measurements

5.1 Effects of CondensableVapors

If the readings of Hastings gauges are to be compared with readings of other types of gauges, consideration must be given to the possible effects of condensable vapors on other gauges. For example, none of the many types of McLeod gauges, give correct readings if condensable vapors such as water, alcohol, acetone, etc., are present in the gauge. The McLeod gauge operates by compressing residual gases and vapors to obtain a reading, and this compression will tend to compress vapors that are present. This usally results in pressure reading that is lower than the actual pressure. Furthermore two different McLeod gauges could be used and both may have different readings. Both of these readings however could be incorrect if vapors are

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