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> From: Hennie Swanepoel <D77190@DVPNFS01.ESKOM.CO.ZA>
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: Current to voltage- anyone know of an IC?
> Date: Wednesday, July 02, 1997 1:43 PM
>
> Tjaart wrote:
>
> > You probably mean 4mA to 20mA, don't you? A 250 ohm resistor gives you
> > 1V to 5V.
> > Even though the 250 ohm is not standard E12, you can still get it in
> > very low
> > tolerances (0.1%).
>
> No, strangely enough 0 to 20mA is an old Siemens standard used for
> process control (on at least some of the South-African power
> stations).  I would pefer not to use only a simple resistor
> (preferably 50 ohm) since the accuracy of (subsequent) A/D conversion
> would be deteriorate due the quantization effect etc. Also I need to
> do the opposite: convert a voltage to a current in the 0 to 20 mA
> range.  The usual solution to both these problems involve using opamp
> circuits.  I was hoping that someone had come around to designing
> IC's dedicated to current/voltage and voltage/current conversion.
>
> Regards
> Hennie

If you are using a micro try looking at the AD420 or AD421 chips from
Analog Devices. They both allow you to generate a current from a 16 bit
digital value

Guy