Current Sensor Output

[Controls1317]

Does anyone have any info on what this guy actually outputs? I know its an analogous number, but what ranges mean what? What conditions trigger a change in the values? What are the actual limits? etc...

[KevinB]

Originally Posted by Controls1317

Does anyone have any info on what this guy actually outputs? I know its an analogous number, but what ranges mean what? What conditions trigger a change in the values? What are the actual limits? etc...

I believe it outputs a value 0-5v that proportionally represents the current detected from 0-75 amps. I haven't actually checked the datasheet or tried to use it, but that is what I've gathered from talking to other people using it.

[Jay Lundy]

Close. It outputs about 0-5V for -75 A to 75 A. 0 A is 2.5V.

There is a graph in the sensor datasheet that shows you the exact voltage vs amps for different temperatures.

[KevinB]

Yep thats it.

[Kevin Watson]

Originally Posted by Jay Lundy

Close. It outputs about 0-5V for -75 A to 75 A. 0 A is 2.5V.

There is a graph in the sensor datasheet that shows you the exact voltage vs amps for different temperatures.

Here's a link to the ACS750 current sensor page at Allegro Microsystems.

-Kevin

[rgengr]

Originally Posted by Controls1317

Does anyone have any info on what this guy actually outputs? I know its an analogous number, but what ranges mean what? What conditions trigger a change in the values? What are the actual limits? etc...

Check out the full datasheet from the Allegro website. The output is half supply (2.5V) for 0 current, and +/- 20mv per amp of current flowing through the large terminals. So, 50 amps would give a 1.5V or 3.5 V output - depending on the current direction through the large terminals. The large current sense terminals are electrically isolated from the three small sensor terminals. Bolt large ring terminals to the PCB for connection to the motor wiring. Pin 1 (with dimple) is 5V, 2 is Gnd, and 3 is the Signal Output. A local bypass capacitor (power supply noise filter) should be placed from 5V to Gnd at the sensor (pin 1 to pin 2). The documentation from FIRST mistakenly shows this across the output terminal to Gnd (pin 3 to pin 2). The value of the power supply bypass capacitor is not critical - anything from 20uf to 200uf, rated from 10V to 25V.

The small PCB does not have to be used - any small piece of PCB material or prototype board can be used to mount the current sensor and provide a means of connection to the pins. In fact, just soldering wires to the terminals would work - if you are careful about soldering. Use enough heat, and be reasonably quick. A helper holding the part with needle pliers held close to the part will hold the part steady - and provide a heat sink between the point being soldered and the body of the part.

The signal output is wired to one of the analog inputs on the robot controller, and 5V and Gnd should be taken from the same connector. A small filter capacitor (perhaps 1nf) placed across the controller analog input to Gnd would help if electrical noise generates inconsistent results.