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Analog and Constant Current Transducers

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New Member
I have a gps system which puts out a DC voltage to a Data Aquisition System with direct relationship to speed. The faster the gps travels the high the voltage. I think its max output is 5 volts.

but my data aquisition system is used to analyze constant current accelerometers.

I want to be able to have my GPS system feed its signal into the DAS so that is know how fast a vehicle is traveling.

Can i feed the DC right into the DAS or do i have to do some type of converting..

I am not familiar with Constant Current. I really dont know what is means. Can anyone explain. All i know is that is uses its power supply lines as its signal lines so only two wires are neede instead of 4.

How can i have my GPS system put out a Constant Current signal?


Well-Known Member
An accelerometer current source is simply the bias current supply for a FET source follower (unity gain amplifier) which resides with the piezoelectric accelerometer transducer. See this link.
The output of the accelerometer is still a voltage. However, if the current source is internal to the A/D converter, you will need to be sure that your GPS output can absorb the bias current (2-4 ma, as I recall) without changing the voltage. An op amp follower (which may already be present) between the GPS and the A/D would solve that problem. Or perhaps you could disable the current source.
The remaining problem is scaling the voltage range of your GPS to that of your A/D input. This could be done with the same op amp, if you know what the ranges are.


New Member
Thank you for that info. I can control the current source going into the transducer. and i do know the scaling. So basicly if i turn off the source of voltage(which will turn the current source off) to the transducer i can use the 2 signal lines as if it were a dataaquisition system setup for a resitive apllication.

In other words i should be able to feed the voltage from the gps directly to my DAS and have no problem as long as the DAS isnt trying to send current to my GPS system.
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