Dynamic Distributors 122A21 manual Helium Bleed Pressure Sensor Introduction, Description

OPERATION MANUAL FOR

MODELS 122A, 122A21, 122A22, and 122A241

HELIUM BLEED PRESSURE SENSOR

1.0INTRODUCTION

The series of sensors described in this guide is designed to measure dynamic pressure in intense thermal environments typified by rocket engine combustion chambers.

These sensors feature acceleration-compensated piezoelectric pressure probes, mounted in a conical end seal helium bleed adaptor.

The helium gas, applied from a 1500 psi source, is metered by a built-in orifice and flows around the probe body and out the passage of the adaptor ahead of the probe diaphragm. The helium gas flowing out the passage protects the sensor diaphragm from the hot gasses as well as increasing the natural frequency of the passage by a factor of approximately three to one.

2.0DESCRIPTION

The model 122A contains a one pC/psi pressure probe (sensor) and is designed to be used with electrostatic charge amplifiers such as the PCB Model 462A.

The Models 122A21, A22, and A24 contain built-in impedance converter electronics circuits which convert the high-impedance voltage from the quartz crystal to a low-impedance voltage signal that can be fed directly into most common indicating or recording instruments.

The 122A series sensors contain a 10 micron helium filter contained in a fitting threaded onto the helium input tube. The purpose of this filter is to prevent particles in the helium supply from plugging the metering orifice.

The outer body of this series is 17-4 PH hardened stainless steel and features a conical tip for sealing without seal rings or washers. This feature also allows the sensor sensing passage to be placed closer to the chamber without a long passage that could cause resonance problems, severely limiting high- frequency response.

Series 122A: Helium Bleed Rocket Motor, ICP® and Charge Sensors

NOTE: The sensor probe in this series is factory installed at a precise depth in the outer body. Do not attempt removal of this probe. Contact the factory should any questions or problems arise concerning the sensor probe.

The Models 122A21, A22, and A23 Sensors use low output-impedance probes (ICP®) and will not require the insulation resistance cautions described for Model 122A.

Connect the sensor cable to the appropriate ICP® power unit and check the front panel monitor meter to check cable connections and internal amplifier.

Consult Guide G-0001B, "General Guide to ICP® Instrumentation" for installation and usage hints for ICP® instruments.

Drawing number: 21089

Revision: NR