Helium Bleed Pressure Sensor

OPERATION MANUAL FOR

MODELS 122A, 122A21, 122A22, and 122A243

4.3OPERATION - ICP® MODELS 122A21, A22, and A24

Consult Guide G-0001B for a complete description of the low-impedance concept in instrumentation.

All PCB power units designed for ICP® use contain built-in fault monitor meters to aid in locating circuit faults (shorts or opens) and to identify normal operation of the miniature impedance converting amplifier built into the sensor.

Do not attempt to apply voltage directly to the input pin of the sensor from any other power source. The input current must be limited to 20 mA maximum and the input voltage must not be higher than 35 VDC. Consult the factory if it is desired to build a power unit rather than to use one of those available from PCB.

The Models 122A21, 122A22 and 122A24 are identical except for sensitivity.

The Model 122A21 has a sensitivity of 20mV/psi which gives a full-scale range (for +5 V out) of 250 psi.

The Model 122A22 has a sensitivity of 1.0 mV/psi and a full-scale range of 5000 psi.

The Model 122A24 has a sensitivity of 5.0 mV/psi and a full-scale range of 1000 psi.

NOTE: Full-scale range is limited by the helium source pressure. The helium source pressure must be at least twice the peak combustion pressure (static plus dynamic) to be measured, but not more than about ten times the lowest pressure.

This is true for all models, charge or ICP®.

5.0CALIBRATION

5.1CHARGE MODEL 122A

To calibrate this model, install in pressure port of dead weight tester and apply various static pressures recording corresponding outputs at each pressure of interest.

Discharge the charge amplifier before each reading and return pressure to zero before each new pressure input.

Use the charge amplifier on "LONG" time constant and keep cables and connections clean to avoid drift.

A D.C. digital voltmeter is ideal for readout during calibration.

NOTE: The helium tube must be plugged with a pressure-tight seal before attempting to calibrate to avoid losing pressure through the helium tube.

If a hydraulic calibration system is used, be sure to remove all traces of oil from the diaphragm passage.

5.2ICP® MODELS 122A21, 122A22 and 122A24

Because of the shorter time constants built into these models, static calibration methods are much more difficult to use.

Pressures must be applied rapidly and readout must be made with fast recording devices such as light storage oscilloscopes or similar types of data acquisition hardware.

A pneumatic (compressed air or hydrogen) system with quick opening valve and reference gage is an excellent method of calibrating these sensors.

To take full advantage of the time constant built into the sensor, use a DC-coupled power unit such as the PCB Model 484B06.

Drawing number: 21089

Revision: NR