We need to get our capacitors calibrated with the following requirements:
1. ANSI/ISO/IEC 17025 Accredited
2. Traceable to NIST (Not NRCC or NPL or any other National Measurement Institute)
3. The capacitance and dissipation cal'd at about 700 V
4. Vendor must be able fill with SF6 gas (5 bar) prior to cal, then reduce SF6 gas to <=1 bar, as they can only be shipped with 1 bar of SF6 gas.
5. Must be able to record pressure measurement indications of internal pressure transducer at calibration test points (pressure reader is supplied with system).
6. Uncertainty approx 25 ppm @ k=2
Anybody know a lab that can cal these to these requirements?
That high accuracy requirement and changing the pressure of the capacitor I beleive is not feasible. A typical temperature dependance of a compressed gas capacitor is on the order of 20 ppm/K so that is allready gonna spoil your accuracy. Not counting the temperature compensated pressure dependance.
My suggestion would be to use a good capacitance bridge and a standard air capacitor like a GR 1404B to calibrate the compressed gas capacitor directly before and after use. With this method you should get below 20 ppm expanded uncertainty.
When purchased, the capacitors came with an analog gauge to monitor the SF6 pressure, we replaced the gauge with a much more accurate transducer. During use, (if we can get these cal'd) we will be sampling the pressure and correcting for pressure differentials. It looks like we may need to do some more research on the temperature dependance (if we can get these cal'd)-thanks for the heads up. We have a GR1689 and AH 2500 bridge, they go no where near the desired 700 V cal potential. A lab (with impeccable credentials) with foreign lab traceability cals these with this method, I would like to adhere to their methodology-they make the majority of the components of the high voltage system. If anyone has anything else to add, it'll be greatly appreciated!