Current Loop Sensor Interface


Posted on Jun 1, 2012

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. This page is technical so that interested persons can build the circuit themselves, but 4QD can also supply the interface on a 'postage stamp' sized (22mm x 27mm) board as shown in the first diagram. It is a relatively trivial circuit! This circuit was developed to interface one of the new type contactless (inductive) throttle sensors to 4QD's motor controllers for use in a conversion to an Eze-Go golf car.


Current Loop Sensor Interface
Click here to download the full size of the above Circuit.

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 microamps 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 sensor will work down to about 5 to 6 volts minimum. 4QD's NCC and Pro-120 use an internal 9v rail, so there is not a huge 'overhead' to allow any voltage swing across the sensor, hence this circuit. The sensor is shown by the standard symbol for a current source (two intersecting circles). 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 practise the customers 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 - 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.




Leave Comment

characters left:

New Circuits

.

 


Popular Circuits

Solar Garden LED Lighting
transistors IR Emitter/Detector with 555 timer alarm
low cost buffered voltage reference
Schematic Diagram LM4992 bassed Stereo audio power amplifier circuit and explanation
LED Lighting For Consumer Unit Cupboard
amstrad cpc464
Portable phone charger



Top