Design of wide-bandwidth analogue circuits for heat transfer instrumentation in transient tunnels
Abstract
The use of thin film surface thermometers to measure heat transfer rates is well established in the Oxford transient Isentropic Light Piston Tunnel, and has been used in many other facilities. In this technique, a resistance-capacitance transmission line, or electrical analog, is used to convert the surface temperature signal into a signal proportional to the heat transfer rate to the surface. This paper describes a new method for designing analogs with a logarithmic scaling of the elements. This uses far fewer elements for a given bandwidth than previous designs and can retain a 1-percent accuracy even when constructed from 20-percent tolerance capacitors, thus eliminating the need for expensive 1-percent tolerance components. A theoretical analysis is given which leads to computer programs to predict the performance of any analog, both in the frequency domain and the time domain. A design example of a low noise analog circuit using only nine sections for a frequency range of 0.1 Hz to 100 kHz is given, together with experimental results showing high frequency heat transfer rate measurements on a turbine blade in the Oxford cascade tunnel.
- Publication:
-
Heat and Mass Transfer in Rotating Machinery
- Pub Date:
- 1984
- Bibcode:
- 1984hmt..book..233O
- Keywords:
-
- Analog Circuits;
- Heat Transfer;
- Network Synthesis;
- Thermometers;
- Thin Films;
- Wind Tunnel Apparatus;
- Capacitors;
- Cascade Wind Tunnels;
- Frequency Response;
- Logarithms;
- Time Response;
- Electronics and Electrical Engineering