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A-4 Field Control™ Genius® Bus Interface Unit User’s Manual
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October 1999 GFK-0825F
A
Measuring Scaling Values
If the circuit will not use millivolt or microAmp units, the most accurate scaling values can be
found by taking actual measurements of the process. The process must be set to two distinctly
different conditions, so two sets of measurements can be taken.
If the analog module is already installed, you can use it online to the process being measured to
obtain actual data values. By default, the Bus Interface Unit performs a 1 to 1 scaling on all
channels. (Using the online method requires the prior configuration of at least the serial bus
address, the I/O map, and the module I/O references).
Finding the Digital Value with the Module Online to the Process
If the module is online to the process, follow the steps below to find the scaling values.
1. Set the process to the first condition to be measured.
2. Using a suitable external device, find the engineering units measurement (for example, PSI, or
degrees).
3. Read the corresponding value with the Hand-held Monitor or the Logicmaster software. The
units (using the default scaling) are millivolts or microAmps.
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using a Hand-held Monitor in default mode, go to the Monitor screens (see chapter 7 if
you need further instructions) and read the channel's digital value.
•
using the Logicmaster software, go to the appropriate data table and read the channel's
digital value.
4. Set the process to the second condition to be measured and repeat steps 2 and 3 to find the
second pair of scaling values.
Finding the Digital Value without the Module Online
If the module is not online to the process, you will need to take two measurements from the
process, and also measure the voltage or current associated with each. Convert this measurement to
millivolts (for voltage) or microAmps (for current).