Voltage error

The differential amplifier compares the attenuated input signal from the detector-amplifier network with the reference voltage, Vq, as illustrated in Figure 6.31. The resulting error signal, V- - Vq, is amp]ified and applied to the servomotor, causing it to move in one direction if the error voltage is positive. 

The slidewire wiper which is mechanically linked to the motor and a pen moves in the direction that will develop a reference voltage equal to the input voltage. This continuous balancing action attempts to cancel the error voltage (V - Vq = 0). The relative motion of the pen and the chart paper results in a plotted graph of response versus time (the chromatogram). 

There is very little loading effect of the current follower circuit. Because the input current source is connected between point S and arinmon and point 5 is kept at virtual common, the input-signal. source senses virtually zero resistance at its output terminals. The effective input resistance R, is the error voltage divided by the input current, i, that is, / , -- v ii.. Because - c,.M atid from Equation 3-4/, - -i jR,. we can write... 

Figure 3.7 Schematic diagram of a phase-sensitive detector at 20 MHz. The transformer is replaced by an active circuit in the HP8709A synchroniser, and probably most high precision configurations. The phase error voltage output is amplified and used in the spectrometer to control the YIG oscillator magnetic field and hence lock the YIG source frequency to the synthesiser frequency. An identical device locks the Gunn MMW source to the YIG frequency (Adapted from Connor )...

The sample temperature is measured by a miniaturized sensor, such as a thermocouple or a platinum resistance thermometer. The sensor voltage is then compared to a voltage set by the experimenter and an error voltage is used to drive current through the heater. For the best precision, three term control is used in which power is reduced as the set temperature is approached and optimum heating is provided to settle on the set temperature. 

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