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2 The controller enters the failure mode.
3 The controller enters the manual mode.
4 The controller enters the calibration mode.
As the Bumpless transfer is activated, the controller will transfer to open-loop control and uses
the previous averaging value of MV1 and MV2 to continue control.
5.2.4.8.1 Without Bumpless Transfer
Since the hardware and software need time to be initialized, the control is abnormal as the
power is recovered and results in a large disturbance to the process. During the sensor breaks, the process
loses power.
5.2.4.8.2 With Bumpless Transfer
After Bumpless transfer is configured with the correct control variables applied, the disturbance
is small when the power is recovered. During the sensor breaks, the controller continues to control by using
its previous value. If the load doesn't change, the process will remain stable. Thereafter, once the load
changes, the process may run away. Therefore, the user should not rely on a Bumpless transfer for a longer
time. For fail safe reason, an additional alarm should be used to announce the operator when the system
fails. For ,a Sensor Break Alarm, if configured, will switch to failure state and announces the operator to use
manual control or take a proper security action when the system enters failure mode.
Warning: After system fails, never depend on Bumpless transfer for a long time; otherwise it might
cause a problem to the system to run away.
5.2.4.9 PV1 Shift
In certain applications it is desirable to shift the controller display value from its actual value. This
can be easily accomplished by using the PV1 shift function. Press the "scroll " key to the parameter SHIF in
card parameter. The value you adjust here, either positive or negative, will be added to the actual value.
The SHIF function will alter PV1 only.
Here is an example. A process is equipped with a heater, a sensor and a subject to be warmed
up. Due to the design and position of the components in the system, the sensor could not be placed any
closer to the part. Thermal gradient (different temperature) is common and necessary to an extent in any
thermal system for heat to be transferred from one point to another. If the difference between the sensor
and the subject is 35 C, and the desired temperature at the subject to be heated is 200 C, the controlling
value or the temperature at the sensor should be 235 C. You should input -35 C as to subtract 35 C from
the actual process display. This in turn will cause the controller to energize the load and bring the process
display up to the set point value
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