Help with AD694 0-10V to 4-20mA V-I Convertor

Hi guys,

I have an application that required a 4-20mA signal to drive a ItoP convertor that in turn drives a control valve.. I'm using Nation Instrument's Compact Field Point AIO610 which has only voltage output of range 0-10.2 Volts.

Therefore I require a V to I Convertor to converter that converts 0-10V to corresponding 4-20mA. For this I'm using an IC - AD694 (Analog Devices) which is a precision V-I Convertor.

AD694 Datasheet

So, here come the major problem. I used this IC and I'm getting 4mA for 0 volts but when I change the input voltage..The output current remains constant. Following are my connections

Pin 1 and Pin 2 Short
Pin 3 - Voltage IN
Pin 13 - 12V DC Supply
Pin 11 - Current Out
Pin 5 and Pin 9 Short

I followed Figure 2 give in the data sheet for the connections. Though with unexpected output..

What really intrigues me is the Pin 7. Should I supply a 10V to that Pin ?? or short it with Pin 8..

I didnt find any other interfacing circuits on the internet. Can anyone figure out what went wrong with the connections ??

I would be very much thankful

Cheers
Posiedon

hi,
If you connect your AD694 as per this circuit from the datasheet you should get 0V thru 10V for 4 thru 20mA.
Leave the 10V force pin o/c

E.

Hi ericgibbs

When I leave PIN 7 (10V Force) open, then the output current is showing 0mA. So I thought it as input and applied 10V to that pin and got 4mA (Lame though ) current for 0v input but when I change the input voltage (0 to 10v), I observed that the current is still 4mA and its not changing for any change in the input ??

I think we have to short 10v force and 2V sense ??

Please check **broken link removed** and this doc (Its for 2V input and they have shorted pin 7 and 8)

Any suggestions ericgibbs ??

megaposiedon said:

Hi ericgibbs

When I leave PIN 7 (10V Force) open, then the output current is showing 0mA. So I thought it as input and applied 10V to that pin and got 4mA (Lame though ) current for 0v input but when I change the input voltage (0 to 10v), I observed that the current is still 4mA and its not changing for any change in the input ??

I think we have to short 10v force and 2V sense ??

Any suggestions ericgibbs ??

Click to expand...

Hi,
The two examples you have posted are for a 2V input range.

Please post your circuit diagram.

Look at this clip from the d/s , the Vref is used for user external circuitry.