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Reference Manual
IP2030/RM, Rev AA
Section 4: Getting started
June 2014
Section 4: Getting started
Signal limits check
The signal is then checked to ensure it is within the range of 3.7 to 20.75 mA. Signals outside
this range cause an alarm condition, which may be externally signalled using a control unit relay
(see “Alarm indication selection” on page 91).
Conversion of signal into a percentage value
By default, the mA signal (readable via D840) is converted (normalized) into a percentage in the
range 0 to 100% (readable via D842), where 4 mA is 0% and 20 mA is 100%.
Note
The control unit can process mA input values in the range 3.8 to 20.5 mA
Read-only parameters D840 and D842 are in the menu MONITOR / DIAGNOSTICS
Applying the optional percentage offset adjustment
P112 is a positive, negative, or zero offset adjustment of the converted (normalized)
percentage. This optional offset feature can be used to accommodate a standing level in a tank.
Note
The output from this adjustment is readable in D802 and is the Tertiary Value (TV) of
the control unit. D802 = D842 + P112
P112 is in the menu SETUP / [CONTROLLER /] INPUT CHANNEL / Ch1 I/P Offset
Applying the scaling factor to get the required units
Changing the PV display units (P200) does not automatically convert the control unit PV to be in
alternative units. A user-entered value in P114 is used to convert (scale) the offset-adjusted
percentage value (D802) to a new value (D801) that is in the required measurement units.
If the mA input represents a liquid level, simply set P114 to the level represented by 20 mA.
Note
D801 is the Secondary Value (SV) of the control unit. D801 = (D802/100) * P114
P114 is not applied if the PV display units (P200) are already configured to be “%”
P114 is in the menu SETUP / [CONTROLLER /] INPUT CHANNEL / Ch1 Pre Scale
Read-only parameters D80* are in the menu MONITOR / READINGS
Optional calculation of contents (volumetric) or flow measurement
By selecting a vessel profile or calculation using P113, a level measurement in D801 can be used
to calculate a volume measurement or open channel flow rate that is then stored in D851.
The programming (configuring) required for this is in “Volumetric contents and flow
measurement applications (advanced users)” on page 52.
Applying an optional low volume or flow rate cut-off action
The channel 1 output result in D851 can be forced to zero when it falls below a positive
threshold, which is a percentage of the maximum flow. Enter the percentage in P117.
By default, the setting is “None” to switch off this optional check.