The circuit described in your scenario is designed to conduct a specific Selection Voltage (SV) test by examining an input signal for certain criteria. Here's a breakdown of the primary functions and objectives of this circuit:
Voltage Threshold Detection:
The circuit uses two voltage comparators (A1AR1A and A1AR1B) to monitor the amplitude of the input signal. Comparator A1AR1A is configured to detect when the input signal falls below -120 mVDC, while comparator A1AR1B is set up to detect when the input signal exceeds +120 mVDC.
Duration Measurement:
Beyond just detecting the amplitude thresholds, the circuit also measures the duration for which the input signal remains beyond the specified voltage thresholds. This is accomplished through a pulse width detector composed of a constant current source (A1Q2), a ramp capacitor (A1C2), and a voltage comparator (A1AR1C).
Simultaneous Conditions Check:
The circuit is designed to flag a failure in the SV test only if both of the following conditions are met simultaneously:
The absolute value of the input signal's voltage exceeds either 120 mVDC or 90 mVRMS.
This amplitude threshold breach lasts for at least 1 millisecond.
Failure Indication:
Assuming there's a digital logic gate and an indicator in the system, upon a failure in the SV test (i.e., both conditions are met), an indication would be given, for instance by lighting up an LED or sounding a buzzer.