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7
4.5 Measuring Temperatures
Each 4500HT pressure transducer is equipped with a Model 4700 vibrating wire
temperature sensor connected to the white and green leads.
A Typical Calibration Sheet is Shown on page 9
5. DATA REDUCTION
The Model 4500HT pressure transducer incorporates a Model 4700 thermometer – both
sensors operating on the vibrating wire principle. The Model 4700 thermometer output
will yield the operating temperature directly using a second order polynomial. Calculation
of the pressure from the Model 4500HT pressure transducer readings is not quite so
direct because the effect of temperature on both the zero reading and gage factor on the
sensors must be taken into account.
Each Model 4500HT pressure transducer/thermometer combination is supplied with a
calibration sheet from the Model 4700 thermometer (see Figure 4) showing the output of
the temperature sensor at 5 different temperatures ranging from room temperature to
250 degrees C. Also supplied are six calibration sheets from the pressure transducer
showing the output readings versus pressure change at each one of these six
temperature intervals. ( Typical Calibration Sheets for the 4500HT transducer are shown
in Figures 5 thru 9).In essence the data interpretation proceeds as follows, using second
order polynomials for greater accuracy:
To calculate the pressure, P, from any current reading, R1, on the pressure transducer.
1. Calculate the temperature, T, from the VW temperature sensor using the output
reading, R
from the temperature sensor and the polynomial expression shown on the
T
temperature gage calibration sheet.
2. Use the temperature values and the zero pressure readings shown on the six
calibration sheets in an Excel spreadsheet to develop a polynomial that describes how
the zero reading, R0, varies with the temperature. (This polynomial will be supplied
along with the cal sheets).
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