Crystal MultiCal Pressure Module - Manual (Page 6)

Calibration  4
MultiCal H2O/PSI Pressure Module Manual
Calibration
—
RECOMMENDED EQUIPMENT
A calibration cycle of 1 year is recommended to maintain the MultiCal within specifications.
Instrument Minimum Specification
Pressure Standard ± 0.025% of Reading
Digital Voltmeter ± 0.025% of Reading with a 10MΩ input impedance
You do not need to use a reference multimeter if the MultiCal will be used with only one multimeter. In those cases, your overall accuracy may be better if it is
calibrated as a set with the matching multimeter.
Many digital voltmeters have a 10 MΩ input resistance. Your reference multimeter should have the same input impedance as the multimeter(s) the module
will be used with. In some cases this may mean that the reference multimeter will need to have its input impedance lowered.
For example, if your reference multimeter has an input impedance of ≥10,000MΩ, and the MultiCal will normally be used with a 10MΩ impedance meter,
simply connect a 10MΩ resistor in parallel with the input to the reference.
—
CALIBRATION PROCEDURE
1 Connect the MultiCal to the pressure calibration system and to the multimeter. Be sure that the pressure calibration system and the connection to the
MultiCal is leak free.
2 Allow the MultiCal to stabilize at room temperature, away from drafts, for at least 30 minutes before proceeding with calibration. Turn on the multimeter
and allow it to warm up per the multimeter operating instruction. Set the multimeter to the appropriate DC volt or millivolt scale.
3 Verify the condition of the battery and replace the battery if necessary. Follow steps 1– 4 of the Battery Replacement procedure to disassemble the Multi-
Cal (do not remove the battery or reassemble the MultiCal).
4 Set the switch on the MultiCal to the Inches H
2
O position (switch in position closest to the banana plugs). Allow the MultiCal to warm up for two minutes.
5 The Fine Zero potentiometer (R1) should be set to the center of its rotational range. To center the Fine Zero, rotate the Fine Zero potentiometer fully clock-
wise until a "click" is heard. Then rotate the Fine Zero potentiometer counter-clockwise 7½ turns. Adjust the Course Zero pot until the output is as close to
zero as possible. Trim in the final reading to 0 mV ±0.01 mV with the Fine Zero potentiometer.