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Chapter 6.0
6.0 Principles of Operation
6.1 General:
This chapter explains in detail how the instrument calcu-
lates mass flow based on specific data input.
Each parameter is updated at a 2Hz rate. Therefore, all
references to the machine's "interval" in the following de-
scriptions indicate a period of 0.5 seconds.
In metric modes, all metric values are converted to En-
glish units internally. The English equations are used to
calculate results. The results are then converted to their
metric equivalent for display.
6.2 Temperature Calculations
If an RTD is used as a temperature transducer, the com-
puter runs a constant current through both the RTD and
the internal precision resistor it is in series with (See
Section 5.12). The computer then measures the voltage
drop across each individually and calculates a ratio, thus
determining the actual resistance of the RTD. A look up
table is used to linearize and convert the ohmic reading to
degrees F.
Any other type of temperature transducer must present a
voltage or current to Channel 1 of the computer. This
value is filtered, digitized and scaled based on the keyed
in temperature parameters. The value is checked against
keyed in alarm limits and the alarm relay is activated if
necessary.
6.3 Pressure Calculations
Any pressure transducer must present a voltage or cur-
rent to Channel 2 of the computer. The raw pressure
value is digitized from Channel 2 and then scaled accord-
ing to the two scale factors to calculate the actual pres-
sure. The value is checked against keyed in alarm limits
and the alarm relay is activated if necessary.
6-1
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