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Hello,
I have got a sensor that outputs a 0 to 1mA DC signal and would like to convert that to 2 to 12V signal, with safe guard limitations to avoid going beyond 0V or above 14V. What sort of circuit/components should I use?
Thanks![]()
hi Eric
thanks for your reply.
The load circuit is to be designed from scratch, it is basicly a block with that 0-1mA signal coming in and 2-12V coming out. It is the detailed circuit for that block that I am struggling with to design.
Cheers
sensor that outputs a 0 to 1mA DC signal
so your source is a 1 mA current source.
to convert that to 2 to 12V signal
"so that we could develop a voltage across a resistor"
(12-2)/1 mA = a 10 kΩ resistor. Shunting the current source with this gives 0 to 10 V out.
Then add an independently powered 2 V level shifter so now we have a 10 kΩ resistor in series with a 2 V source (use one of those LMxxx adjustable bandgap references) to ground, so now we have 2 - 12 V out with 0 to 1 mA in.
Add any diode in series with the 0-1 mA current source so that the 2 V source can't push current back into the 0-1 mA current source.
So far no power gain or impedance level changing is necessary.
Drawing 10 µA by loading this circuit with a 1.2 MΩ resistor will give you a 1% output voltage error.
If the load resistor is smaller than 1.2 MΩ you need a current amplifier (emitter follower or opamp voltage follower).
hi willbe,
This will only work, if the sensor suppy voltage to the sensor is at least [10V+ Voltage required by the sensor]
and the output impedance of the sensor is low.
hi,Hi, Mr. G!
If the sensor really is an ideal current source it has infinite output impedance and an infinite open-circuit voltage. Real world current sources bring up the issue of compliance. This link is kind of weird but it does explain the basic idea. http://www.keithley.com/data?asset=6465
In the worst case, probably he should use an opamp as a current-to-voltage convertor and stick in a level shifter somewhere in the feedback loop. He might then need dual supplies. It gets messy quickly.
With no constaints yet on accuracy I'd kind of like to squeeze as much as I can out of the source, first. If the load is a DMM, we're almost done.
Willbe, which of your 2 solutions do you recommend for the 'ideal' design purpose and which in case I ever get around and actually build it?
Eric, I didn't understand what you meant by your second post, about the voltage overhead, can you elaborate more please?
A schematic will be brilliant!
Thank you so much!
Thank you Willbe for the schematic, I was able to retrieve it, however when I tried to simulate it, the result seemed a bit strange, it is mostly in the voltage shifter. I have uploaded my design and simulation results in an album called "i2v", will be you be kind enough to have a look and tell me where I went wrong?
Eric, I do apologise, but I am still a bit struggling to follow you up with the overhead voltage. I got lost after "If however the sensor required only 5volts to operate correctly, it would still have a 4volt 'overhead' to drive the 1mA loop." If 1V is measured already across the 1000R resistor (which is what I am after) and the sensor got its 5V to operate, what will be the problem with the overhead 4V?
Cheers
Thank you Willbe for the schematic, I was able to retrieve it, however when I tried to simulate it, the result seemed a bit strange, it is mostly in the voltage shifter. I have uploaded my design and simulation results in an album called "i2v", will be you be kind enough to have a look and tell me where I went wrong?
Eric, I do apologise, but I am still a bit struggling to follow you up with the overhead voltage. I got lost after "If however the sensor required only 5volts to operate correctly, it would still have a 4volt 'overhead' to drive the 1mA loop." If 1V is measured already across the 1000R resistor (which is what I am after) and the sensor got its 5V to operate, what will be the problem with the overhead 4V?
Cheers
the 2 upper schematics in your diagram, that these are the voltage shifter and would fit in with the voltage across the 10K resistor to produce the required 2 to 12V, please correct me if I am wrong.
Not sure what do you mean by the diodes being 2V ref voltage.
How do you do the attached thumbnail that can be expanded? I hate posting mostly white paper.