We are working with a board that I have seen mentioned on this forum before. It is a current sensing modeule (Model YYI-2) that allows you to set a threshold current value and if that current is exceeded it closes a relay contact on the board. We are trying to use it on a stepper motor driver that runs a motor that opens or closes a needle valve. We need to detect when the valve fully closes and stalls the stepper motor. We have an existing closure detector consisting of a micro switch that trips when the valve drive gear lowers to the closed position but that approach relies on mechanical adjustment and we can never adjust it to the fully closed position accurately. The current sensor module works great except for one problem. We connect one to a setup and when powered up the digital readout of load current says 0.15 (150 ma). When we exercise the stepper motor the readout goes to 250 ma. We set the trip point to 270 ma and we can exercise the drive motor without the relay tripping and when we drive the motor to the valve closed position and the motor stalls the relay trips telling our PLC to stop the motor. All well and good except we try board number two and now the static currenr reading is 300 ma. We try another and the static reading is 260 ma. Five boards and all with different current readings. We have an ammeter connected and the static current is always 140 ma. Evidently these boards need base calibration. Any one know which fixed resistor we may have to play with?

 

We are working with a board that I have seen mentioned on this forum before. It is a current sensing modeule (Model YYI-2) that allows you to set a threshold current value and if that current is exceeded it closes a relay contact on the board. We are trying to use it on a stepper motor driver that runs a motor that opens or closes a needle valve. We need to detect when the valve fully closes and stalls the stepper motor. We have an existing closure detector consisting of a micro switch that trips when the valve drive gear lowers to the closed position but that approach relies on mechanical adjustment and we can never adjust it to the fully closed position accurately. The current sensor module works great except for one problem. We connect one to a setup and when powered up the digital readout of load current says 0.15 (150 ma). When we exercise the stepper motor the readout goes to 250 ma. We set the trip point to 270 ma and we can exercise the drive motor without the relay tripping and when we drive the motor to the valve closed position and the motor stalls the relay trips telling our PLC to stop the motor. All well and good except we try board number two and now the static currenr reading is 300 ma. We try another and the static reading is 260 ma. Five boards and all with different current readings. We have an ammeter connected and the static current is always 140 ma. Evidently these boards need base calibration. Any one know which fixed resistor we may have to play with?

I doubt anyone can help without a schematic, or at least a good photo of the PCB.

 

Module: https://alexnld.com/product/yyi-2-5...-protection-board-current-sensor-relay-board/

IA: MAX472 datasheet https://pdfserv.maximintegrated.com/en/ds/MAX471-MAX472.pdf

 

Thanks for providing the MAX472 spec sheet. It looked like the best way to calibrate would be to use a 5K trimmer for Rout off pin 8. We did this and were able to make a small adjustment off the 2K fixed resistor vaue to make our static current on the YYI-2 board agree with the digital ammeter. But now the motor running current is off (130 ma versus 280 ma actual). So now we have a linearity problem. We adjusteed the pot to make the running current agree but now the static current is off (170 ma versus 130 ma actual. We probably should be using a different set of resistors for the current range we are operating in but to do that would be too much chopping on the board.

 

You know that how current is measured is one problem.

Your DVM could be TRMS and therfore doing a good job. MOST DVM's basically average: Precision rectifier and a capacitor multipled by a fudge factor so that a sine wave input reads RMS. You feed it PWM and you get a repeatable, but random number. Frequency matters too. Your DVM will also insert a shunt.

The MAX472 is also an obsolete part.

it great you knew what to do with the pieces. You knew more than you let on. Next time. https://lmgtfy.com/?q=max472+datasheet

Hint: you can also search http://images.google.com I didn't.

 

Many circuits under current monitoring may happen be rather high freq - 20 kHz, 200 kHz or even 6 MHz. Whilst the most of current monitoring sensors with a hard goes over 50 Hz. Just study Your sensor datasheet about speed and make an averageing until it works correct. Look on signals by good fast oscillo, probably the spikes are factor making the trouble. Then apply the block capacitors.

 

Thanks but this application is for pretty clean 24 VDC.

 

Then ask why most of ferrite trafo suppression circuits at SMPS using 1 kV capacitor when Vcc is just 310V.