Hmmm.. it’s a magnetic sensing component, you seem to have it clamped in a huge block of ferrous material (the vice). Does it read different away from the vice ?
The rubber pads on the vise jaws likely provide enough distance that the steel would have little influence. I suppose it is possible that the steel has become quite strongly magnetized, but that would almost certainly produce an offset error rather than a gain error.
It's likely a mislabeled acs704 or 706, both have a 133mv/A sensitivity. Check the resistance between pins 6 and 7, on the 704/706 they're shorted together. The 704/706 are discontinued so are probably dirt cheap.
Assuming the IC is authentic, the device in datasheet quite clever. It has a hybrid of electrical chopper-stabilize & Hall offset auto null in-one. So the opamp offset auto-nulls at the same time as the magnetism canceled out. Not only that but works like this over temperature range. That makes the zero signal output = 0.5 Vdd. Failure of this chopper stab would cause the output to be offset from 0.5 Vdd and drift much more than spec. I reckon you can test for defective chopper by watching the zero-current signal drift with temperatura and chsnge of external field magnetic.
Beware of those boards !.... Several years ago I bought from AliExpress plain ACS712-05 chips and found them OK BUT...a few months ago I bought 3 times from different vendors this kind of board with ACS712-05. They were OK about the scaling factor but the outputs were so noisy that, to use them, I had to heavily filter the output for lowering that noise (and bandwith as well). The datasheet says noise = 21 mVpp max for a 2 kHz bandwith... I had more than 100 mVpp noise with a Cfilter = 47 nF, that means an equivalent noise of more than +/-0.5A reading... The chip is built around a chopper amp and I guess that the ones that I bought were rejects from the factory. These boards are therefore only usable for very slow signals (& DC of course)
@@IMSAIGuy in UK dot is the separator between integer and decimal parts ;-) But other countries in Europe use coma as separator. World is strange: billion = milliard etc. ;-)
2.1kV... the discussion was about the separator but there I put it right for you and I give shit loads of shit about a shit load of shit...actualy ;)@@zyghom
One of the graphs in the datasheet says it should be pretty much bang on 2.500 V for no current (at 5V bias, 25°C) and going below freezing should still kick it off less than 10mV I can't even conceive how the user could mess with that (short of wrong supply, but you said you set it to exactly 5V so ¯\_(ツ)_/¯ )
These sensor modules are rather popular, meaning it is likely that they are highly faked. The part series is very wide... 712, 714, 724, on and on. Still available on Mouser, last I checked.
Is there a part specified at 135 mV/A? Possibly, the chip's label is wrong. Is there possibly a shunt so that not all of the current goes through the chip? Is it reasonable that the current is not divided equally between the two pin pairs? This might make the magnetic field's distribution problematic.
The IC output is RATED as HALF the supply voltage with no current flowing, so the accuracy and stability of its supply would affect its output. This is not unusual in this sort of ICs.
You obviously have some nonmagnetic causes going on, which, according to the datasheet, causes the quiescent output voltage to deviate, which needs to be factored in the calculation using the ratiometric calculations, accuracy graph etc. Or it may just be rubbish.
Without an internal voltage reference, the 1,5% accuracy become the smallest problem ^^ So it would be better if it e.g. requires 5V makes a 3.3v reference or something and measures this against…
This chip has ratiometric output from supply voltage. In many cases it is better than using a internal voltage reference. If the ADC uses the same supply voltage as reference as the sensor then the dependence on the reference voltage disappear. If it had an internal reference then errors in both the internal reference and the reference for the ADC would add to the sensor error.
@@larslindgren3846 okay yeah correct but i would never use a supply voltage as my reference voltage not even in rapid prototyping it’s 2-5 more lines of code if internal in uC MSP432 in my case.
@@steinmar2 If you for some reason (e.g. other sensors that has absolute voltage output) uses a reference voltage other than supply voltage in the ADC then you can compensate for the supply voltage simply by measuring it with an other ADC chanel and calculate the ratio. From a theoretical point of view it is better to measure the ratio of two signals than an absolute voltage. Many precision measurements are made ratiometric e.g. strain gauges, temperature, differential transformer sensors and other measurement bridges. Ratios can theoretically be self calibrating while a voltage reference needs traceable calibration to an primary voltage standard.
@@larslindgren3846 One important caution with use of the supply rail as a reference, even in ratiometric circuits, is to be sure the supply is adequately clean and stable at the relevant physical locations in the circuit and at the relevant times. The latter is important if you want to calculate the ratio of two signals. Sampling both as closely spaced in time as possible is generally best. Collect both samples, _then_ do any required processing. If you do something like reading multiple times to get an average, interleave the readings of the two channels, don't do all the samples for one then move on to the other. Don't forget that "calibration" in code can result in missing counts. Offset correction is usually easy and clean. Gain (scale) correction often isn't. The resistance of the wires used to connect to a bridge device can introduce significant error in some instances. This can often be fixed with four-wire schemes and some good instrumentation amps carefully applied.
@@d614gakadoug9 Good points but at 1.5% accuracy I don't think they mater most of the time. In a high accuracy situation all relevant sources of errors need to be considered. A separate clean reference for the sensor and the ADC is a good idea. The point is that you don't want to have two separate voltage references for the sensor bridge and the ADC since errors in the voltage references then directly translates to measurement errors.
I had good success with ADS1261. Used +/-5V for excitation and +/-2.5V for the ADC analog section, but you can just use clean +5V for excitation and the ADC, except that the you will get double the noise/signal ratio. I run it at 500Hz with circular STM32 DMA and it can go much faster.
@@IMSAIGuy I would vote for out of spec because its deviation is very accurately the same in both directions and is very linear when you double the current, which would hardly be the case with a poorly made copy. I am actually amazed how well it tracked the current changes - the AMOUNT of change per ampere is not a big deal when you can always adjust your circuit for that, either in hardware or in code. Out of spec would also be consistent with what we often get from AliExpress as one guy accurately put it: factory floor sweeping specials, meaning masses of out of spec rejects are sold cheaply BECAUSE they couldn't be sold as such otherwise.
