Pressure Units with a Pirani Vacuum Transducer & ADC-16

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Pressure Units with a Pirani Vacuum Transducer & ADC-16

Post by SteveHansen » Tue Mar 02, 2004 3:59 pm

I am trying to apply an MKS model 907 convection vacuum transducer to an educational application. The transducer has an output that ranges from about 0.3 volts at the low end (corresponding to 0.001 Torr [mmHg]) to 5.666 volts at the upper end (1000 Torr). In between the voltage - pressure correspondence is very non-linear (sort of a lazy "S" with a tail) but the manufacturer provides an adequate table. The curve can also be expressed by two equations, one for the lower end of the transducers range, the second for the upper end.

Logging voltage vs time is no issue except that the output of the transducer has to connect to the differential inputs of my ADC-16 via a resistive voltage divider to keep the range within 5.0 volts.

However, for use with pressure units that axis will have to cover 6 decades so a log scale is needed. I looked in the software documentation and I couldn't find a way to do this. at least not without writing code (which I have never done).

Any suggestions?

Steve Hansen

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Post by markspencer » Wed Mar 03, 2004 9:05 am


In Picolog it is possible to put in your own scaling file, the one supplied by the manufacturer. However, first you will need to calculate the value from the reduced value bck to it original value, this can be done with a formula, the calculated parameter can then have a scaling factor applied.

I would suggest looking at Picologs help manual under scaling.

Best regards,

Mark Spencer


Post by SteveHansen » Wed Mar 03, 2004 9:02 pm

Thanks, I just printed out the whole manual and will look at it again over the next few days. I'll let you know how I make out.

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