Crystal MultiCal KPA/PSI - Manual (Page 5)

PN: 1763 Rev C, 4/2004
Page 5 of 8
C R Y S T A L
engineering corporation
MultiCal Calibration
A calibration cycle of 1 year is recommended to maintain the MultiCal within specifications.
Table 1: Recommended Equipment
Instrument Minimum Specification Recommended Model
Pressure Standard ± 0.025% of Reading DH Instruments PPC2+
Digital Voltmeter
± 0.025% of Reading
10MΩ input impedance
Fluke 45
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.
The recommended Digital Voltmeter listed in Table 1 has 10MΩ input impedance - as
do many handheld multimeters. 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, a Fluke 8840A is an excellent benchtop meter, but it has an input impedance of
≥10,000MΩ. If the module will be normally used with a lower impedance meter, like a Fluke
87, which has an input impedance of 10MΩ, simply connect a 10MΩ resistor in parallel with
the input to the 8840A.
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 the Battery
Replacement procedure to disassemble the MultiCal, but do not remove the battery or
reassemble the MultiCal.
4. Set the switch on the MultiCal to the kPa 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 clockwise until a “click” is
heard. Then rotate the FINE ZERO potentiometer counter-clockwise 7½ turns. Adjust
the COARSE 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.
6. Check the kPa pressure points shown on Table 2. Adjust R12 if necessary to bring the
readings to within the tolerances shown on Table 2.
7. Set the switch on the MultiCal to the PSI position.
8. Test the MultiCal at the 30 PSI point. The reading should be within the tolerance shown in
Table 2. If not, adjust R15 until both points are within specification.
9. In the unlikely event that you are unable to adjust the MultiCal so that all of the points
meet the tolerances of Table 2, contact Customer Service for assistance. Do not readjust
linearity. The linearity adjustment is factory set and should never require readjustment,
unless the sensor is replaced.
Figure 1: Potentiometer Locations
FINE ZERO
kPa
PSI
COARSE ZERO
-
LINEARITY
R1
R12
R15
Table 2: Readings in mV @ 23°C ±5°C
True Pressure Acceptable Output (mV)
100 kPa 99.92 to 100.07
200 kPa 199.87 to 200.12
30 PSI 29.98 to 30.03
Specifications
The following specifications apply at 23°C, ±5°C for 1 year after calibration, and when
used with measuring devices having 10MΩ input impedance, or shunted so that their input
impedance is 10MΩ. Also, the module must be "zeroed" prior to taking measurements to
achieve the pressure specifications.