The signal to be measured is fed into the input of the Signal Amplifier. The output of the DC amplifier is a DC voltage proportional to measured voltage. This voltage is available at the output connector.
The Signal amplifier is an AC voltage amplifier, which includes a low-noise instrumental differential amplifier, precision amplifier with selectable gain and a bandpass filter. The gain is set using the switch installed on the front panel. Gain 1, 10, 100 and 1000 can be set to provide a wide range of input signal levels. The bandpass filter cuts off signals with frequencies below 150 Hz, including the main and double frequency of the mains voltage, as well as signals with frequencies above 1200 Hz to reduce noise in the measured signal.
The phase sensitive detector PSD is a circuit which takes in two voltages as inputs Vsignal and Vreference and produces an output which is the product Vsignal * Vreference. That is, the PSD is a multiplier circuit.
The low pass filter is a higher-order active low-pass “many pole” filter whose time constant may be selected. The time constant is set using the switch installed on the front panel.
The DC amplifier is a low-frequency amplifier with selectable gain. It differs from the Signal Amplifier in that it works all the way down to zero frequency (DC) and is not intended to work well at frequencies above 10 KHz. Gain 1, 2, 4 and 8 can be set.
The Chopper is designed to modulate an optical signal at the input of a spectral instrument. The Chopper Controller sets the modulation frequency and maintains it with high accuracy using an optical sensor. The Chopper Controller also generates a reference signal for both lock-in amplifiers.