Pressure Decay - Leak Standard Calibration

The pressure decay - leak standard test is used to determine a leak flow rate calculated by the instrument from the pressure loss  measurement during the test time. CTS Sentinel instruments are equipped with an absolute pressure transducer that measures the delta pressure loss (psig) and converts that measurement to a flow rate (scc/m). For accuracy the instrument needs to be calibrated with a known non-leaking test part to perform the conversion. Once the calibration is complete, converting the delta pressure to a flow rate is performed automatically by the instrument.  

Chart showing the slope of leak rate vs. pressure loss.

How to Perform Pressure Decay Program Calibration

To prepare for calibration, the instrument must be set up for the correct test pressure and a repeatable leak testing sequence that includes fill, stabilize, test, exhaust and relax timers. This process can be conducted manually or by utilizing a CTS unique “Auto Setup” program where the instrument sets each of these timers automatically with simple operator interface.

Once complete, the operator will utilize a master part placed into the test fixture and press the instrument auto-calibrate button:

  1. A non-leaking master part is tested to establish the “Zero Leak” setpoint (master part loss).

  2. The master part is tested with the leak standard included in the test circuit to determine the maximum acceptable leak rate (master + leak loss).

Using these setpoints the instrument establishes the ‘Target Flow Window’ for a pressure decay flow leak test.  

Pressure Decay Leak Standard Calibration Cycle

Two charts side-by-side, with first one showing the calibration cycle for a master part and the other the second calibration cycle with the master part and leak standard
The test cycle fills a test part to a specified test pressure, the test part is isolated from source air, test pressure stabilizes, and the pressure decay test is run. The instrument measures the delta pressure loss and correlates it to flow units and reports the results of the test. If the flow rate is within the acceptable leak rate flow limits, the part passes the leak test. If outside the target limits, the part fails the leak test and is rejected. 
Chart showing pressure over time in a pressure decay with leak standard calibration test.

 Tips to Conduct and Validate a Reliable Calibration

  • It is important to utilize a known non-leaking production part as a master part
  • The leak standard should be certified and within its dated certification window
  • The relax timer should be long enough for the master part to exhaust fully and achieve ambient temperature status
  • Check the final performance factor “PF” instrument feedback to verify the calibration cycle is acceptable
  • Utilize master “good” and master “reject” parts with leak standards below and above the reject limits to validate a calibration process 

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