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Documenting Process Calibrator
Using Source Mode
45
Providing Loop Power
The calibrator provides loop power at 28V or 24V dc.
The 28V setting provides enough current for two or
three 4-20 mA devices on the loop in addition to the
two-wire transmitter but uses more battery power.
Use the 24V setting if there are two or fewer loads on
the loop in addition to the two-wire transmitter. (Each
device on a typical 4- to 20-mA loop has a resistance
of 250
Ω
, thus dropping 5V at 20 mA. A typical
transmitter must have 11V minimum in order to
operate correctly at its top end.)
When loop power is enabled, the mA (middle
column) jacks are dedicated to sourcing and
measuring the current loop. This means that the
SOURCE mA, measure RTD, and measure and
source
Ω
functions are not available (see Table 8,
later in this manual.)
Connect the calibrator in series with the instrument
current loop as Figure 16 shows. Proceed as follows
to source loop power:
1. Press s for s mode.
2. Note that following Loop Power, Disabled is
highlighted. Press e.
3. Use the u or d arrow keys to select Enabled
24V or Enabled 28V.
4. Press e.
5. Press the Done softkey.