Electromechanically Stabilized D.C. Amplifier for Use in Transducing and Telemetering of Milli-Voltage and Micro-Ampere Signals

This amplifier as presently designed with the available type of deflecting meter can reliably, within the specifications, amplify direct input voltages and currents as small as 5 millivolts and 20 micro-amperes, respectively. It appears that the limitation on increasing the sensitivity is basically the increased effect of meter friction which in turn causes the unit to be more vibration and position sensitive. This amplification is linear, stable and free of drift. In addition, the mechanical nature of the amplifier limits the frequency of the input to a few cycles per second. Nevertheless, in the higher ranges, this unit offers a compact and simple amplifier which is continually stabilized by the electromechanical action of a deflecting meter movement. The capacity pick-up design of position, which adds only a small constant force to the delicate meter suspension, is extremely simple and appears to have infinite resolution. The only critical components are easily obtained stable resistors which are the only components pertinent to calibration. These resistors can be so modified in value as to permit any type of input range or combination thereof by means of a selector switch. For use with thermocouples the use of a very stable and compact mercury cell for cold-end compensation makes the unit independent of cold end temperature variations. The input circuit (depending upon the type of measurement) offers either a very high or very low impedance to the source, making the unit suitable for amplifying a wide variety of electrical phenomena.