Figure 2 shows a typical circuit, using a source-follower connection to the internal MOSFET with a 200 kΩ load. The output from the detector is amplified in two stages of a quad operational amplifier, with a voltage gain, overall, of around 3200; the gain is controllable by the variable resistor in the feedback circuit of IC2. The output from IC2 is passed to a threshold circuit, using a 220kΩ variable resistor to set the threshold voltage at which signals will be passed to the output transistor Tr1, which will amplify and shape the output from the detector. The output is shown operating an LED display with an output to an alarm circuit. In use, the alarm will be turned off when not needed, but the LED is usually kept in operation to indicate that the unit is working correctly.