HP T100 Spécifications télécharger pdf (Page 23)

The elevated zero at atmospheric pressure for a 0.1-5.1 Vdc unit is:

Elevated Zero = 0.1V + (Slope) x (abs. value of full vacuum. - abs. value of available vacuum)

As an example, assume that -13.7 psig is available and the desired zero level corresponds to -14.7

psig. Full scale is 30 psig.

The zero output at -14.7 psig is 0.1 Vdc. The full scale output at 30 psig is 5.1 Vdc.

Slope = (5.1 Vdc - 0.1 Vdc)/(14.7 psig + 30 psig) = 5 Vdc/44.7 psig

The reading at -13.7 psig = 0.1 Vdc + (5/44.7) x (14.7-13.7) = 0.2119 Vdc

To check span, first make sure no pressure leaks are present before making this calibration.

Next, apply full scale pressure from a traceable, certified and calibrated pressure source and

adjust to 5.000 Vdc output if required. Recheck zero and adjust again if necessary.

Diagnostic Shunt

This transmitter has an ability to check itself for zero and span. This quick check can be done to

determine if the unit is functioning properly. It should not be used to set the pots except in an

emergency as it doesn’t have the accuracy of a field or factory calibration. Apply power to the

transmitter. Remove the pot access cover. The two terminal shunt pins are located above the

potentiometers. To use the shunt to check zero, first vent the pressure port and check for 4 mA

(4-20 mA output) or 0.1 Vdc (0.1-5.1 Vdc) for 0 psig based units or

For vacuum referenced ranges, you must calculate the proper offset for the calibrated range.

Diagnostic Shunt (4-20 mA output)

Calculate the slope of output current vs. pressure:

Slope = mA span output current / pressure of full span

The elevated zero at atmospheric pressure:

Elevated Zero = 4 mA + (slope) x (absolute value of full vacuum pressure)

The following is an example for a Vac to 30 psig factory calibrated as -14.7 psig to 30 psig:

Zero (at -14.7 psig) = 4 mA

Full Scale (at 30 psig) = 20 mA.

Slope = (20 mA-4 mA)/(14.7 psig + 30 psig) = 16 mA/44.7 psig

The reading at 0 psig or atmospheric pressure is:

Elevated Zero = 4 mA + (16 mA/44.7 psig) x (14.7 psig) = 9.26 mA

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HP T100 Spécifications Page 23