Red Lion TSC - Manual (Page 32)

INPUT MODULE (1- IN) (Cont’d)
Input Sensor Correction Constants (SPAN & SHFt)
If the controller temperature disagrees with a reference temperature
instrument or if the temperature sensor has a known calibration, the controller
temperature can be compensated by a correction slope (SPAN) and offset
(SHFt).
SPAN - 0.001 to 9.999
SHFt - -999 to 9999
The following equation expresses the relationship:
Desired Display Temp = (Controller Temp x SPAN) + SHFt
EX1.) The controller reads 293°F while a reference instrument indicates
300°F. A SHFT value of +7°F corrects the controller indication to match
the reference. (Use SPAN = 1.000)
EX2.) A thermocouple probe is calibrated over the region of operation to
achieve more accurate temperature control. The calibration results are as
follows:
Desired Temperature Thermocouple Output
400.0F 395.0F
800.0F 804.0F
SPAN = 800F - 400F = 0.978
804F - 395F
SHFT = 400F - (0.978 x 395F) = 13.7°F
SPAN value of 0.978 and SHFT value of 13.7°F corrects the indicator to
the probe.
Setpoint Limit Values (SPLO & SPHI)
The controller has programmable high and low setpoint limit values to restrict
the setting range of the setpoint. Set the limit values so that the temperature
setpoint value cannot be set outside the safe operating area of the process.
SPLO - -999 to 9999
SPHI - -999 to 9999
Auto Setpoint Ramp Rate (SPrP)
The setpoint can be programmed to ramp independent of the controller’s
display resolution. The setpoint ramp rate can reduce thermal shock to the
process, reduce temperature overshoot on start-up or setpoint changes, or
ramp the process at a controlled rate
SPrP - 0.1 to 999.9 degrees/minute
A ramp value of zero disables setpoint ramping. If the user input is
programmed for setpoint ramp, it affects the enabling and disabling of setpoint
ramping (refer to user input section). Setpoint ramping is initiated on
power-up or when the setpoint value is changed and is indicated by a decimal
point flashing in the far right corner of the main display.
Note: The auto setpoint ramp rate is independent from the operation of a profile.
Once the ramping setpoint reaches the target setpoint, the setpoint ramp rate
is disengaged until the setpoint is changed again. If the ramp value is changed
during ramping, the new ramp rate takes effect. If the setpoint is ramping prior
to invoking Auto-Tune, the ramping is suspended during auto-tune and then
resumed afterward using the current temperature as a starting value. Deviation
and band alarms are relative to the target setpoint, not the ramping setpoint. If
the analog output is programmed to transmit the setpoint value, the
instantaneous ramping setpoint value is transmitted.
Note: Depending on the ramp rate relative to the process dynamics, the actual
process temperature may not track the ramping setpoint value.
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