A computer program has been developed to shorten the time needed to set up electronic instrumentation for a hot-fire test of a rocket engine. The instrumentation in question is a modular, partly computer-controlled apparatus, the modules of which contain amplifiers and other signal-conditioning circuits. The apparatus processes signals from strain gauges and other sensors.

The Option Byte Calculation subprogram generates this display. This subprogram calculates the value of the byte needed to balance a bridge circuit in a strain-gauge module.

Before

this program was developed, the modules could be set up only through a controller front panel. Signals from external sources were introduced by unpatching input terminals and applying the signals to amplifiers. The strain-gauge modules are programmed digitally by use of bytes called "option bytes." Before the program was developed, the values of option bytes needed to balance strain-gauge bridge-circuit readouts were found by trial and error. In the case of a thermocouple signal conditioner, it was necessary to disconnect cables to read the true output voltage. For these and other reasons, the time needed to set up the instrumentation for each test was too long.

The program can be used to set up every module needed for a test. Both the amplifier and the remaining signal-conditioning circuitry in each module can be adjusted by use of this software. Each module can be programmed for any desired gain setting and calibration step. It is no longer necessary to resort to trial and error to balance strain-gauge bridge circuits (see figure). Programmable strain-gauge-balance reports and system-status reports can be generated to reduce setup time. The program can display real-time data, both numerically and graphically, and can display the internal memory of the test apparatus; these capabilities can be utilized to diagnose any suspected defect in a measurement or in the entire testing system.

A unique feature of this program is that setup information is sent from the computer that runs the program, via a serial communication port, to a hand-held "dumb" terminal that includes a small display screen and a keypad, which resembles that of a pocket electronic calculator. This feature makes it possible to perform the test setup from either the computer or the dumb terminal. The dumb terminal displays as many as four lines of information from a test-setup-window display on the computer terminal. Each key on the keypad corresponds to a button in the test-setup window. A technician can easily move to and adjust a module while viewing the display on the dumb terminal.

This work was done by Michael W. Burge of Rocketdyne Division of Rockwell for Stennis Space Center.

Inquiries concerning rights for the commercial use of this invention should be addressed to

the Technology Transfer Office
Stennis Space Center
Attn: John Bailey (228) 688-1660

Refer to SSC-00093

NASA Tech Briefs Magazine

This article first appeared in the December, 1999 issue of NASA Tech Briefs Magazine.

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