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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.
Figure 4-32.With Bumpless Transfer
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.
4.3.1.1.4.9 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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