Crystal nVision Lab Reference - Manual (Page 49)

Support  47
nVision Operation Manual
Support
—
TROUBLESHOOTING
The nVision is a very high performance reference recorder. Due to the high resolution of this product, you may observe conditions that appear to be defects in the
product, but are in fact a result of being able to read and measure pressure to a degree not possible with other instruments.
Noisy or unstable reading when used with fluids
When calibrating or comparing the indicated pressure from an nVision against a hydraulic deadweight tester or piston gauge, the reading on the nVision may
appear unstable—the least significant digit jumps up and down several counts.
 Reason
Gas (usually air) is trapped in the line between the nVision and the deadweight tester. What is actually happening is the mass is oscillating up and down, and
the combination of gas and fluid is acting like a spring. At higher pressures (above 2000 PSI, typically) this may eventually diminish, as the gas dissolves into
the fluid.
 Solution
Evacuate all tubing with a vacuum pump before introducing fluid into the system.
Non-repeatability of pressure measurements
When checking the gauge against a hydraulic deadweight, increasing pressure measurements do not match decreasing pressure measurements.
 Reason
As in the previous note, gas has dissolved into the hydraulic fluid. When decreasing the pressure, the dissolved gas then leaves the fluid, but at an uneven rate,
so a small pressure differential (due to fluid head pressure) may exist between the reference deadweight and the gauge being tested.
 Solution
Evacuate all tubing with a vacuum pump before introducing fluid into the system.
Slow return to zero and/or non-repeatability of pressure measurements
 Reason
Pressure port is obstructed.
 Solution
Clean with low pressure fluid. Do not touch diaphragm as damage will result.