Figure 1. Strain Gauge Sensor principal of operation.
Most errors in pressure transducers are caused by non-linearity (the deviation from a
straight line relationship of output voltage over the full operating pressure range),
hysteresis (the difference in a pressure reading when approached from maximum pressure
as opposed to approached from minimum pressure), and non-repeatability (the maximum change
in output under the same operating conditions over a specified time period).
The type of diaphragm contained in VMC Pressure Transducers minimize non-linearity.
The molecularily-bonded strain guauge elements in VMC Pressure Transducers significantly
reduce hysteresis and non-repeatibility.
With the typical foil strain gauge sensor, the major source of non-stability is creepage
of the adhesion between the foil and the diaphragm. When the sensor stays at one position
for a long period of time, the adhesion tends to relax, especially under high-temperature
conditions. This can cause up to a 10% bias (zero pressure reading) shift. With VMC Pressure
Transducers, there is typically less than a 1/2% bias shift.
During laboratory testing in which transducers are exposed to 250 degree (F) temperatures
for 48 hours with 80% full-scale pressure applied, VMC Pressure Transducers will typically
shift less than 1%, whereas other strain-gauge transducers will typically shift in the 10% range.
VMC Manufactures pressure transducers in the following ranges:
60 psi, ¼” NPT Male
100psi, ¼” NPT Male
200psi, ¼” NPT Male
500psi, ¼” NPT Male
750psi, ¼” NPT Male
1000psi, ¼” NPT Male
2000psi, ¼” NPT Male
5000psi, ¼” NPT Male
7500psi, ¼” NPT Male
Transducer Models
All VMC pressure transducers are manufactured with a 316 stainless steel body and a ¼ NPT Male
pipe thread connection. VMC Manufactures three different models of transducers in a variety of
pressure ranges. There are two different connector styles available, and an external calibration
block can be specified. The pressure sensing elements, electronics, and peformance charateristics
of The three models of transducers are:
Model 852
The VMC Model 852 transducer has a 3 Pin Sure Seal connector, with a 24” pigtail.
This was VMC’s standard pressure transducer for many years.
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Model 992
The VMC model 992 transducers has a 6 pin military spec connector built into the body of the
transducer. This provides superior strain relief and electrical shielding.
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Model 988
The VMC Model 988 transducer has the built in 6 pin military spec connector, as in the Model 992,
with the addition of a calibration block giving access to trim pots for bias and offset adjustment.
Most VMC systems have software calibration routines, which eliminate the need for making
calibration adjustments to the transducer, however if your application requires field calibration
of transducers, then the VMC model 988 is the correct transducer.
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