I have a project that would need to measure plus or minus ~100 milliamps. Instead of designing my own circuitry I'd be willing to bet that there is a chip that would do a good job. My problem is googling those terms is a bit overwhelming. Can anybody recommend a device capable of positive and negative current measurement in that range? 1 mA resolution would be sufficient.
Additionally I also plan to output a +- 100 mA signal with 1mA resolution. Again I could kludge some circuitry together, but if someone knows of a device that is capable of the task, I'd be miles ahead.
OP asked for current measurement, not voltage measurement.
Sense resistor must be as low as practically possible to not influence the circuit (not 50 ohms).
Differential A/Ds (ADS1115) usually can't work with negative voltages,
so a differential A/D might not work.
OP, we need to know the details of your circuit for meaningful advice.
Leo..
The project is going to intercept and hijack the control signal of a CIS-E fuel injection control module to the electrohydraulic actuator. The actuator is a 19.5 ohm coil typically driven with less than +- 100 mA.
I'm not asking how to do it. I just don't want to go through the chore of designing, debugging, and calibrating the circuitry to find out after the fact that x chip could do it with minimal effort. If it were only dealing with positive currents, it would be simple enough, but adding the complexity of reading and outputting negative currents begs the question, is there a chip that can do either, easily?
As said, the INA219 can measure bi-directional currents, with a resolution of 0.1mA, and better if needed.
But that current line always needs to be positive (high-side).
What is needed is a circuit diagram or datasheet, showing how that 'thing' is driven (H-bridge?).
Constant voltage/current, PWM, otherwise.
Maybe current measurement is not the only way to get the info needed.
Probably can't help you much there, because I don't know what part you're talking about.
Leo..
duxthe1:
The project is going to intercept and hijack the control signal of a CIS-E fuel injection control module to the electrohydraulic actuator. The actuator is a 19.5 ohm coil typically driven with less than +- 100 mA.
I'm not asking how to do it. I just don't want to go through the chore of designing, debugging, and calibrating the circuitry to find out after the fact that x chip could do it with minimal effort. If it were only dealing with positive currents, it would be simple enough, but adding the complexity of reading and outputting negative currents begs the question, is there a chip that can do either, easily?
So the voltages will be within the 0 -- 13.8V range of a car battery? INA219 should be fine then. How
did you arrive at +/-2V ?
Can you clarify the bandwidth or sample rate you require? How many samples?
Measuring 100mA is not an issue.
Finding 100mA current source is not an issue.
Finding a 15V 1 to 100mA current source ?
That's an issue.
Most of them are much lower voltage.
MarkT:
So the voltages will be within the 0 -- 13.8V range of a car battery? INA219 should be fine then. How
did you arrive at +/-2V ?
19.5 ohm load driven to 100mA The electrohydraulic actuator is a 19.5 ohm coil that controls the cross section of a small orifice. It's neutral position is partially open and is driven closed with negative current of about 50mA and driven further open by positive currents up to around 75mA.
I intend to read how the CIS module drives this actuator and output my own signal to control it. Most of the time I'll be mirroring the CIS but under certain conditions (high engine load) I'll be outputting my own desired control signal. The signal is a constant current so bandwidth won't be an issue. As fast as the Arduino can run the loop will be more than sufficient in terms of how quickly I'll be altering the signal.
I think you have gone completely off the road.
The IN219 is just a measuring device. It is not a current source.
19.5 ohm load driven to 100mA
Why are you talking about driving a load in response to Mark's comment about the IN219A ?
Are you answering his question about the +/- 2 ?
E = I*R
Let R = 19.5 ohms
Let I = 0.075A
then:
20*.075
ans =
1.5000
E = V = 1.5V
The load needs to be driven by a precision current source (the same one you said you would be needing)
The IN219A has nothing to do with that. It is your current measuring device.
The electrohydraulic actuator is a 19.5 ohm coil that controls the cross section of a small orifice. It's neutral position is partially open and is driven closed with negative current of about 50mA and driven further open by positive currents up to around 75mA.
This suggests an H-bridge is driving it but the the H-Bridge source is probably the current source so it's
a current source with an H-bridge on the output. How else is it getting negative current ?
If you look at a schematic of any part of an automobile you see a positive V+ and a chassis GND.
In that environment, if you need to drive an inductive load in both directions, you have to use an
H-bridge.
H-bridge?
Maybe it's variable PWM, and NOT a variable current at all.
If you measure PWM with a DMM (which averages), then you see a varying voltage/current.
Better connect a scope to it.
Leo..
I've worked with these systems for 20 years, it's a positive and negative current, not a variable PWM. I've brought a CIS module home so I can trace the circuit and draw a schematic.
Given the contention and lack of simple solutions offered, I'm guessing there isn't an easy route. If feasible I may just copy the circuit from the CIS module for the output and do something like dual op amp circuit with an inverting and non inverting output for the current measurement.
What do you expect with no schematic of the circuit you are trying to replace ?
If it was that simple then why did you post ?
You asked for a chip, I gave you one. LT3092
Mark gave a chip to measure the current.
If you've worked with these systems for 20 years then why can't you tell us how it reverses the current
in terms of a schematic ?
What are you expecting , a drop in replacement for an unknown circuit ?
Is the zero volt reference of the actuator power
supply available so the driving voltage and polarity
can be measured or do you just have 2 wires going
from the driver to the actuator?
Is -40 ma or +60 ma a viable current?
raschemmel:
What do you expect with no schematic of the circuit you are trying to replace ?
If it was that simple then why did you post ?
You asked for a chip, I gave you one. LT3092
Mark gave a chip to measure the current.
If you've worked with these systems for 20 years then why can't you tell us how it reverses the current
in terms of a schematic ?
What are you expecting , a drop in replacement for an unknown circuit ?
I'm not asking for a replacement of a circuit, I'm asking is there is a chip that can read positive 100 mA to negative 100mA with 1mA resolution, and is there a chip that can source the same?
I've not seen one posted that meets either criteria.
I'm not aware of any schematic that exists of the circuitry I'm looking to emulate. I will trace and sketch the schematic, myself. Meanwhile after 20 years troubleshooting the vehicles thusly equipped, I do know that it delivers a current and not a pulsewidth.
We need to know which potential those two actuator connections are on.
So is one grounded, and the other one +2volt to -2volt relative to ground.
Or are both connected to mid supply (of the car), and each terminal is deviating from that.
Without knowing reference voltages, we can't give a solution.
Chips DO have a working window (common mode range).
The window of the INA219 I suggested is 0-26volt.
Leo..
I'm asking is there is a chip that can read positive 100 mA to negative 100mA with 1mA resolution, and is there a chip that can source the same?
To my knowledge , you have not stated how you would control the bidirectional current source.
I also do not recall you explaining what you plan to do with the measured current.
As I understand it , you have simply stated the need to measure current and the need to source current but have not connected the dots.
I am wrong please show me where you explained that part.
How does this explain what you do with the measured current and the criteria for controlling the current. ?
(I'm not an automotive person I don't anything about the CIS control module )
The project is going to intercept and hijack the control signal of a CIS-E fuel injection control module to the electrohydraulic actuator.
You guys are overthinking this. A module controls a valve. I'm going to put my piggyback module between the first module and the valve. The piggyback will measure the first module's current output. Software will decide the desired current and then the piggyback will output its own current to control the valve.
If a current sensor exists that can read + and - 100mA, that would simplify the current measurement part. My option is to measure positive current with 1 analog pin and then invert the negative current reading and measure that, costing another analog input pin, and it will all need some amount of calibration. Hey, maybe I'll ask the forums if something like my theoretical current sensor exists to make life easy.
Likewise, outputting a + or - current will have to get split into 2 functions. I wonder if there is a chip that could do that without a lot of fuss?