WCS 1800 35A Current sensor

Thread Starter

TMK3252

Joined Nov 30, 2016
13
the sensor is giving too much noise when i measure a dc current of 1A. i have connected a value of 1uf 63v electrolytic capacitor in parallel with 100nf ceramic capacitor.

the connection diagram and the oscilloscope output is attached here.

the sensor output is for zero current.

help me.

Murali.
 

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LowQCab

Joined Nov 6, 2012
4,218
You probably have a problem with how You are using your Oscilloscope.

High-Frequency-Noise can not make it past those Capacitors.

The Output from this Device needs to be Buffered with an Op-Amp for best performance.
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Thread Starter

TMK3252

Joined Nov 30, 2016
13
You probably have a problem with how You are using your Oscilloscope.

High-Frequency-Noise can not make it past those Capacitors.

The Output from this Device needs to be Buffered with an Op-Amp for best performance.
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requesting a little explanation.

how can i add the buffer with op amp.
 

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Hymie

Joined Mar 30, 2018
1,288
According to the data sheet, you should be measuring 66mV with a current of 1A.

First check your 5V supply for noise (this may very well be the source of the issue).

The data sheet recommends a capacitor value of 10 – 100nF, whereas you have 1µF.

What is the nature of the current you are measuring, and its frequency?
 

Hymie

Joined Mar 30, 2018
1,288
According to the data sheet, at 0A the output should be around 2.5Vdc (which is what you have) with a typical output noise of 3mV (with a 10nF capacitor); your scope is showing 3.3mV rms (although the peak to peak noise is just over 200mV).

So the current sensor appears to be working within spec for a zero current.
 

nsaspook

Joined Aug 27, 2009
13,442
requesting a little explanation.

how can i add the buffer with op amp.
You don't need a buffer for the sensor output as it's already a buffered output from the driver circuit. I'm not sure of the source of the noise pulses every few tens of microseconds but the source is unlikely from the Hall sensor. Be sure to have a 0.1uf bypass cap at the sensor for vcc and gnd in case there is power supply noise. For low noise and stable reading the sensor needs to be mounted on a proper PCB.
I usually have a dedicated 5vdc high precision ratiomatic power supply bus just for Hall sensors that's decoupled from the controller 5vdc supply to eliminate these sorts of power supply related drift and noise issues.
https://www.ti.com/lit/ds/symlink/ref02.pdf
1706745719622.png

The quality of the sensor also makes a huge difference.
https://forum.allaboutcircuits.com/...c-controlled-battery-array.32879/post-1496750
1706744633044.png
Honeywell CSLT6B100 100A zero current voltage. SD of 86 microvolts, very good. https://sensing.honeywell.com/CSLT6B100-open-loop-current-sensors
 

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Thread Starter

TMK3252

Joined Nov 30, 2016
13
According to the data sheet, you should be measuring 66mV with a current of 1A.

First check your 5V supply for noise (this may very well be the source of the issue).

The data sheet recommends a capacitor value of 10 – 100nF, whereas you have 1µF.

What is the nature of the current you are measuring, and its frequency?

hello thanks for the reply

i am measuring DC current. and i have taken 5V supply from the controller.should i take isolated 5 v power supply?
 

Hymie

Joined Mar 30, 2018
1,288
A simple way of removing the signal noise is to feed the output through a resistor (say 10kΩ), after which place a capacitor to ground (say 10µF) and measure the signal across the capacitor. With the above component values the output signal will have a 0.1s time constant, which should remove the noise you are seeing.

If you need more damping, increase either the resistor or capacitor value.

If having a high resistance in the output signal line won’t work for your circuit, feed the signal into a buffer op-amp to increase the available output current.

If the speed of response of the circuit is important, you may need to experiment with resistor and capacitor values to optimise the response versus signal noise.
 

Hymie

Joined Mar 30, 2018
1,288
Here is the complete noise filter circuit, including a buffer op-amp.

If powering the op-amp from the 5V supply, you might need to select an op-amp that can drive its output rail to rail, otherwise its output voltage swing is likely to be limited to ~3V.

By selecting the optimum values for R and C you should be able to reduce the signal noise significantly while maintaining a reasonably fast circuit response.
 

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Thread Starter

TMK3252

Joined Nov 30, 2016
13
According to the data sheet, at 0A the output should be around 2.5Vdc (which is what you have) with a typical output noise of 3mV (with a 10nF capacitor); your scope is showing 3.3mV rms (although the peak to peak noise is just over 200mV).

So the current sensor appears to be working within spec for a zero current.
Here is the complete noise filter circuit, including a buffer op-amp.

If powering the op-amp from the 5V supply, you might need to select an op-amp that can drive its output rail to rail, otherwise its output voltage swing is likely to be limited to ~3V.

By selecting the optimum values for R and C you should be able to reduce the signal noise significantly while maintaining a reasonably fast circuit response.
i will try this one ..Appreciating your inputs

Thank you Very much
 

Thread Starter

TMK3252

Joined Nov 30, 2016
13
If you're using a controller ADC to read the sensor voltage it's easy to use a simple software low pass 'noise' filter to smooth out actual random noise and to 'average' the signal response of the Hall sensor.
https://www.edn.com/a-simple-software-lowpass-filter-suits-embedded-system-applications/

I tried this ...the noise almost reduced.

for zero current it is reading 2.6346v to 2.6369v.

how can i set the offset in esp32 for current which is varying from 4.5A to 5.5A in the code?

how can i approch this via code in esp32?
 

nsaspook

Joined Aug 27, 2009
13,442
I tried this ...the noise almost reduced.

for zero current it is reading 2.6346v to 2.6369v.

how can i set the offset in esp32 for current which is varying from 4.5A to 5.5A in the code?

how can i approch this via code in esp32?
The ESP32 type ADC's are well known for being crap.

The quick and dirty way is to calibrate the system with two known values set as constants in the program. The zero offset (an ADC reading with zero current) and a scalar (typically a multiplier value) for a standard signal from that offset the gives the correct value of units needed, Amps here.
 

Thread Starter

TMK3252

Joined Nov 30, 2016
13
The ESP32 type ADC's are well known for being crap.

The quick and dirty way is to calibrate the system with two known values set as constants in the program. The zero offset (an ADC reading with zero current) and a scalar (typically a multiplier value) for a standard signal from that offset the gives the correct value of units needed, Amps here.
Can you suggest any ADC controller which is not like ESP32(Crap) to measure a current up to 10 amp.

suggest me a sensor and controller.
 

nsaspook

Joined Aug 27, 2009
13,442
Can you suggest any ADC controller which is not like ESP32(Crap) to measure a current up to 10 amp.

suggest me a sensor and controller.
It's (ESP32 ADC) just noisy and non-linear but most of those problems can be mitigated with processing and using the center of the ADC range as is usually the case with a ratiomatic current sensor.
https://aylo6061.com/2022/05/27/arduino-esp32-samd21-ads1015-adc-comparison/

You should be able to make a decent system with what you have.
 
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