The NASA Lewis Strain Gauge Laboratory: An update

Efforts continue in the development and evaluation of electrical resistance strain gauges of the thin film and small diameter wire type. Results obtained early in 1986 on some Chinese gauges and Kanthal A-1 gauges mounted on a Hastelloy-X substrate are presented. More recent efforts include: (1) the determination of the uncertainty in the ability to establish gauge factor, (2) the evaluation of sputtered gauges that were fabricated at Lewis, (3) an investigation of the efficacy of dual element temperature compensated gauges when using strain gauge alloys having large thermal coefficients of resistance, and (4) an evaluation of the practical methods of stabilizing gauges whose apparent strain is dependent on cooling rate (e.g., FeCrAl gauges)

Evaluation results of the 700 deg C Chinese strain gauges

Gauges fabricated from specially developed Fe-Cr-Al-V-Ti-Y alloy wire in the Republic of China were evaluated for use in static strain measurement of hot gas turbine engines. Gauge factor variation with temperature, apparent strain, and drift were included. Results of gauge factor versus temperature tests show gauge factor decreasing with increasing temperature. The average slope is -3-1/2 percent/100 K, with an uncertainty band of + or - 8 percent. Values of room temperature gauge factor for the Chinese and Kanthal A-1 gauges averaged 2.73 and 2.12, respectively. The room temperature gauge factor of the Chinese gauges was specified to be 2.62. The apparent strain data for both the Chinese alloy and Kanthal A-1 showed large cycle to cycle nonrepeatability. All apparent strain curves had a similar S-shape, first going negative and then rising to positive value with increasing temperatures. The mean curve for the Chinese gauges between room temperature and 100 K had a total apparent strain of 1500 microstrain. The equivalent value for Kanthal A-1 was about 9000 microstrain. Drift tests at 950 K for 50 hr show an average drift rate of about -9 microstrain/hr. Short-term (1 hr) rates are higher, averaging about -40 microstrain for the first hour. In the temperature range 700 to 870 K, however, short-term drift rates can be as high as 1700 microstrain for the first hour. Therefore, static strain measurements in this temperature range should be avoided

The NASA High Accuracy Fuel Flowmeter (HAFF) Development Program

The high accuracy fuel flowmeter development program is described. A flightworthy meter that measures mass flowrate of aircraft fuels to within + or - 0.25% of reading over a 50:1 range of flow is developed. A study of measurement techniques to achieve this goal yielded three candidates: (1) a dual turbine flowmeter with density and viscosity compensation; (2) an angular momentum flowmeter with a motor-driven, spring-restrained turbine and viscosity shroud; and (3) a vortex precission flowmeter with density and viscosity compensation. An experimental study of each technique was completed and the first two candidates were selected for prototype development

An automated secondary standard for calibrating liquid flowmeters

A secondary working standard of flow calibration has been developed to be used in place of a primary weight-time standard, and which can thereby effect a 75 percent reduction in calibration time while maintaining acceptable accuracies. The secondary standard uses six previously calibrated turbine-type flowmeters built into two manifold systems containing automatically switched flow valves. The pair of systems is capable of covering the flow range of 0.0004 to 19 l/s (0.007 to 300 gpm) with the uncertainty in volume flow rate not exceeding + or - 0.25 percent over the range of 0.06 to 19 l/s and not exceeding + or - 0.5 percent over the range 0.0004 to 0.06 1/s. Data reduction and plotting of results are by computer

Use of small turbine-type flowmeters to measure flow in large pipes

Measurement of mass flow in large pipes using small turbine-type flowmeters is discussed. Experiments for determining accuracy of flowmeter and applicability to various types of flow measurement are reported. Illustration of turbine flowmeter and calibration curve are included

Liquid flow sight assembly Patent

High pressure liquid flow sight assembly for wide temperature range applications including cryogenic fluid

Small turbing-type flowmeters for liquid hydrogen

Characteristics of turbine-type flowmeters in two sizes and with various types of bearings are presented. Calibration procedures of instruments are described. Accuracies obtainable under various conditions are analyzed

Life tests of small turbine-type flowmeters in liquid hydrogen

A total of 14 turbine-type flowmeters of 2.5- and 4-cm nominal size were operated for 100 or more hours at an average fluid speed in the unobstructed, upstream pipe of 20 m/s for the smaller meters and 9 m/s for the larger meters. Calibration shifts over a 6.1 range of calibration flow rates varied from 0.5 percent to 1 percent after 50 hr of operation. It is concluded that use of ball bearings with glass-filled Teflon retainers is most likely to produce minimal calibration shift with protracted use. Bearing replacement after 50 to 100 hr is recommended, depending on accuracy requirements, for meters used at the fluid speeds of the tests

Evaluation results of the 700 deg C Chinese strain gages

There is a continuing interest and need for resistance strain gages capable of making static strain measurements on components located in the hot section of gas turbine engines. A paper by Tsen-tai Wu describes the development and evaluation of high temperature gauges fabricated from specially developed Fe-Cr-Al-V-Ti-Y alloy wire. Several of these gages and a quantity of P12-2 ceramic adhesive were purchased for evaluation. Nine members of the aircraft turbine engine community were invited to participate in an evaluation of these gages. Each participant was sent one strain gage, a small amount of ceramic adhesive, instructions for mounting the gage on a test beam, and a set of suggestions for the experiment. Data on gage factor variation with temperature, apparent strain, and drift are discussed

Advanced high temperature heat flux sensors

To fully characterize advanced high temperature heat flux sensors, calibration and testing is required at full engine temperature. This required the development of unique high temperature heat flux test facilities. These facilities were developed, are in place, and are being used for advanced heat flux sensor development