Current Loop Light Level Detector

Description: This circuit is a two-wire light level detector, which does not separate the wires for power supply and output signal delivery. It operates using a current loop that performs both functions over a single pair of cables, requiring only a voltage supply while measuring the current as the output signal. The core of this circuit is the LM10 voltage reference and operational amplifier integrated circuit (IC).

This circuit operates in a floating mode, where shorting the supply pin to the output pin disables the upper half of the final push-pull output stage within the IC. This configuration leads to the output current becoming independent of any positive input signal, resulting in a fixed quiescent current drawn from the loop. When a negative signal is applied to the input, the final output stage activates and generates a saturated current in response to input voltages as low as a few hundred microvolts.

The use of the LM10 as a voltage reference ensures stability and precision in the detection of light levels. The operational amplifier within the circuit amplifies the differential signal from the light sensor, enabling it to respond effectively to variations in light intensity. The current loop configuration allows for long-distance signal transmission while minimizing the impact of noise, making it suitable for various applications, including industrial automation and environmental monitoring.

The circuit design emphasizes efficiency and reliability, ensuring that the output signal can be accurately monitored and measured without interference from the power supply. This makes it a valuable tool for engineers and technicians working in fields requiring precise light level measurements.This circuit is two wire light level detector, we don`t separate wires for power this sensor system and for delivering the output signal. With current loop, we do both function in a single pair of cable, just provide the voltage supply and measure the current as the output signal.

The core of this circuit is LM10 voltage reference and op-amp integ rated circuit, operating in floating mode. By shorting the supply pin to the output pin, the upper half of the final push-pull pair inside the IC will be disabled, making the output current is not related with any positive input signal, so a fix quiescent current will be drawn from the loop. At negative signal of the input, the final stage begin working and will produce saturated current at few hundreds micro-volts input.

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