This is a very simple circuit to interface a current loop sensor to an input which is designed for a voltage, such as that from a standard potentiometer. The circuit is based on five transistors. They will amp the input that is entered the circuit. This is the figure of the circuit.
The operation of this circuit is Tr1 and Tr2 are a current mirror arranged to source about 1mA into the sensor, via Tr2. This current can be adjusted by the preset to 'back-off' the zero position current. This allows an electrical zero adjust (in practice we usually prefer to use the throttle's mechanical zero adjust). Tr3, 4 and 5 are a second mirror which reflect the sensor's output current (less the backed off zero portion) into the 4K7 resistor is a resistor is a current to voltage converter. We have therefore developed an output voltage proportional to throttle position and it has the same 3 wires as a standard potentiometer.
The throttle itself consists of a coil and some electronics with a steel jacketed brass slug which is moved in and out of the coil by the throttle movement. The assembly has only two contacts and draws a current of between 600 micro amps and 2 milliamps: the current varies with slug position as the throttle is moved. As such it is a system which borrows much from the industrial 4-20mA current loop sensor standard.
The operation of this circuit is Tr1 and Tr2 are a current mirror arranged to source about 1mA into the sensor, via Tr2. This current can be adjusted by the preset to 'back-off' the zero position current. This allows an electrical zero adjust (in practice we usually prefer to use the throttle's mechanical zero adjust). Tr3, 4 and 5 are a second mirror which reflect the sensor's output current (less the backed off zero portion) into the 4K7 resistor is a resistor is a current to voltage converter. We have therefore developed an output voltage proportional to throttle position and it has the same 3 wires as a standard potentiometer.
The throttle itself consists of a coil and some electronics with a steel jacketed brass slug which is moved in and out of the coil by the throttle movement. The assembly has only two contacts and draws a current of between 600 micro amps and 2 milliamps: the current varies with slug position as the throttle is moved. As such it is a system which borrows much from the industrial 4-20mA current loop sensor standard.
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