Shunt Calibration Features in High Accuracy Transmitters

Engine Test Solution

Viatran Models 422/423 is the preferred pressure transmitter for Engine test engineers because of three main reasons:

Compact Size

Viatran Models 422/423 have a diameter of 7/8" and a standard length of 3.78 inches. Small size has the benefit of allowing more sensors to be installed per a finite area, thus enabling more measurements to be taken and more room in the test cell area for other devices.

High Accuracy

Test cells need very precise measurements. The 422/423’s piezoresistive sensors with fully compensated programmable electronics provide optional accuracy error as low as ±.04%. Better measurements are equivalent to higher quality data, and when making decisions related to product features and compliance requirements, it provides better understanding of performance tradeoffs.

Fair Price

Models 422/423 offer a simple design targeted to the test cell application. Features, which users have been advised are not a requirement for optimal performance in test cell environments, have been pared away in order to achieve a fair price for the performance.

The Issue

A large engine manufacturer approached Viatran regarding additional options to further improve 422/423’s performance in their test cells.

The quality process involved in the calibration of test equipment is meticulously carried out. To streamline the procedures involved, a review of the QC checks was undertaken. One item that was identified to improve the process was the ability to verify that the electronics in the sensor are functioning to specification before actually submitting the units to pressure in the process. Over time, the customer has determined that regular re-calibration of the sensor is not needed, as the “as found” condition of the transducer will pass virtually 100% of the time if the sensor/system passes their QC test. A transmitter with shunt calibration is part of the process that allows scrutinizing the electronics.

The Solution

Add three shunt calibration choices to Models 422/423, available as optional upgrades.

Depending upon the requirement, one of three shunt calibration types is available:

The internal shunt calibration (Code DE) sets a resistance of 80% of FSO on the side of the bridge when the user shorts connector pins 5 and 6. For verification purposes, the value for every unit is laser etched on the housing of Models 422/423.

The internal isolated calibration option (Code DA) employs an optoisolator chip, which is mounted on an independent PCB in the transmitter. The board applies voltage to activate the shunt again at 80% of FSO. The isolation of the shunt cal provides improved noise immunity as it is isolated from the sensor circuit.

An externally powered optically isolated shunt calibration (Code LV), uses an isolated circuit to function, but is activated by applied voltage from an external source. Shunt cal value is once again standard at 80% of FSO. The isolated circuit excludes potentially noise inducing ground loops.

There is a solution for individual QC test with several shunt calibration options now available for Models 422/423.

This information has been sourced, reviewed and adapted from materials provided by Viatran.

For more information on this source, please visit Viatran.