Low control point: Note that when controlling from a higher pressure to a lower pressure, the lowest controllable pressure is is 400 psig (27 bar).
The most likely causes of poor control are the following:
- air in the system
- air in the DUT/UUT manifold
- insufficient volume - min 50cc
- control tuning
- insufficient drive pressure
Verify the following:
1. Drive pressure is 90-110 psi
- If drive pressure is too low the isolation valves will not stay closed.
- If the drive pressure is too high it will actuate the pressure relief valve.
- Recommend 1/4" to 3/8" hose OD, the larger the better.
2. Minimum volume of 50cc connected to test port
- The control tuning at the factory is done with 50cc volume.
- Increasing volume or air in the system will increase control times and may affect control stability.
3. No air in the system
- Purge all air out of the system. See this article, 7615 Rupture Disc Replacement, and purge trapped air
- Consider Fluke PN 3882774 7615-EXV, External bleed valve kit
4. Leak Test - DO NOT CHANGE TO MEASURE MODE AT FULL SCALE (MAX) PRESSURE - may blow burst disc
- Leak test at around 90-95% FS. When the controller is set to measure mode, there is displacement from the isolation valve closing and you will see the pressure increase by approximately 5% and this may cause the rupture of the burst disc if you are at full scale pressure.
- To perform leak test, control to a pressure for about 2 minutes, go to measure mode, let pressure stabilize for about 5-10 minutes. Take minimum of 60 seconds of data and ensure leak rate is better than 0.04%FS/minute
Additional Troubleshooting found at the following article