Question

How is the ZMO value derived with Endevco absolute pressure transducers? I have an 8515C-50 transducer with a ZMO specified on the cal cert. Is this value recorded at atmospheric pressure?

Answer

The short answer is No. The ZMO value is recorded at 1psi vacuum. Further explanation is needed to clarify why 1psi vacuum and not 0 psi. It is not possible on earth to achieve true zero pressure. From a practical standpoint with our manufacturing and test equipment we use 1 psi vacuum and use a BFSL (Best Fit Straight Line) calculation to determine what the ZMO value is for the specific serial number transducer being manufactured /tested. The calibration certificate expresses the calculated BFSL ZMO from the linearity BFSL. The user will need to correct the Full Scale Output reading by accounting for the ZMO identified on the cal cert. The ZMO may be either a positive or negative value. Endevco transducers also specify the thermal zero shift and zero shift after 3x FSO (Full Scale output).

Endevco absolute pressure transducers use an evacuated hermetically-sealed sensing module which is then epoxy-sealed to the case of the transducer. For PSIA units (absolute) the reading should be equal to the calibrated sensitivity (mV/psia) x local atmospheric pressure plus the calibration certificate ZMO specified. If a PSIA unit had a sensitivity of 4 mV/psi, a reading of 58.8 mV plus the ZMO specified would be acceptable for 14.7 atmospheric. Re.Endevco Dynamic Pressure Measurement Technology Textbook, 1991

See sample cal cert excerpt below for highlighted ZMO.