Crystal GaugeCalXP - Manual (Page 7)

Operation  5
GaugeCalXP Operation Manual
10 Start the test: We recommend that you exercise the gauges by applying the full scale pressure of the gauge being tested, one or more times. To apply
pressure to the gauges, wind the handle in a clockwise direction. To decrease pressure to the gauges, wind the handle in a counter-clockwise direction.
After decreasing the pressure to zero, recheck the fl uid level in the reservoir, and rezero the Crystal reference gauge, if necessary. You will notice that the
application of pressure is non-linear, therefore pressure increases at a more rapid rate at higher pressures.
11 Compare pressure readings: Wind the handle clockwise on the comparator so that the needle on the device under test is centered on the fi rst major gradua-
tion mark (or fi rst calibration point). These major marks are usually placed at 10% or 20% increments of the full scale of gauge being tested. Hold the pressure
for 15 seconds, then compare the pressure on the device under test to the pressure displayed on the Crystal reference gauge, and record the reading.
Checking the accuracy of an analog pressure gauge against the display of the Crystal reference gauge
Normally, pressure will drop at fi rst, as each ascending pressure point is reached. This is due to the residual, trapped gas, fi rst heated by compression, then
cooled, so that the compressed gas is at the same temperature as the ambient environment. An equal and opposite eff ect happens when reducing pres-
sure—the pressure will rise as each new lower pressure is achieved. Waiting for these thermal eff ects to stabilize can add a lot of time to the calibration.
12 Quick test method: An alternative method eliminates the time required to wait for thermal pressure stability. This method works with the Crystal XP2i and
nVision, but not with the 30 Series. Start by setting the Crystal reference gauge to detect peaks and clear any stored peak value. As above, increase pressure
to the fi rst major graduation on the device under test (or to the fi rst calibration point), but increase pressure slowly, so that you don’t overshoot the mark
(or point). The maximum pressure recorded on the Crystal reference gauge will be the pressure that was applied—even if actual pressure drops again im-
mediately. Just record the peak reading from the Crystal reference gauge and continue to the next test point or mark. If you are also checking the gauge for
hysteresis, the procedure is the same, except that you start at full scale and check the Crystal reference gauge for the Peak Lo. Eliminating the time required
to wait for thermal equilibrium, signifi cantly shortens the amount of time it takes to calibrate a gauge.
Note: The Fine Adjust option (PN 3205) may be mounted on either side of the GaugeCalXP. The ports for the Fine Adjust are located behind removable side
plates at the rear of the comparator.
Note: If you cannot generate the desired pressure it is for one of two reasons: Either the system has too much air in it, or the volume being pressurized is too
large. Use the procedure on the following page to remove more air from the system or to generate vacuum.