Tempco tec-220, Instruction Manual, Page: 19 / 36

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3–8 PV Shift
In certain applications it is desirable to shift the
controller display value from its actual value. This
can easily be accomplished by using the PV shift
function.
The SHIF function will alter PV 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 (differing temperatures)
is common and necessary to an extent in any ther-
mal 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 enter -35°C 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.
3–9 Digital Filter
In certain applications, the process value is too unstable to be read due
to possible electrical noise. A programmable low-pass filter incorpo-
rated in the controller can be used to improve this. It is a first-order
filter with the time constant specified by the FILT parameter. The
default value of FILT is set at 0.5 seconds before shipping. Adjust
FILT to change the time constant from 0 to 60 seconds. 0 seconds
means no filter is applied to the input signal. The filter is characterized
in Figure 3.8.
Note
The filter is available only for PV, and is performed for the displayed
value only. The controller is designed to use unfiltered signal for con-
trol even if the filter is applied. A lagged (filtered) signal, if used for
control, may produce an unstable process.
3–10 Failure Transfer
The controller will enter failure mode if
one of the following conditions occurs:
1. SBER occurs due to input sensor break
or input current below 1mA if 4–20 mA
is selected or input voltage below 0.25V
if 1–5V is selected.
2. ADER occurs due to the A-D converter
of the controller failing.
Output 1 and output 2 will perform the fail-
ure transfer function as the controller
enters failure mode.
Output 1 failure transfer , if activated,
will perform:
1. If output 1 is configured as proportional
control (PB≠ 0), and BPLS is selected
for O1FT, then output 1 will perform
bumpless transfer. Thereafter, the previ-
ous averaging value of MV1 will be
used for controlling output 1.
2. If output 1 is configured as proportional
control (PB≠ 0), and a value of 0 to
100.0% is set for O1FT, then output 1
will perform failure transfer. Thereafter,
the value of O1FT will be used for con-
trolling output 1.
3. If output 1 is configured as ON-OFF
control (PB=0), then output 1 will be
driven OFF if OFF is set for O1FT and
will be driven ON if ON is set for
O1FT.
Output 2 failure transfer , if activated,
will perform:
1. If OUT2 is configured as COOL, and
BPLS is selected for O1FT, then output
2 will perform bumpless transfer.
Thereafter, the previous averaging
value of MV2 will be used for control-
ling output 2.
2. If OUT2 is configured as COOL, and a
value of 0 to 100.0% is set for O2FT,
then output 2 will perform failure trans-
fer. Thereafter, the value of O1FT will
be used for controlling output 2.
3. If OUT2 is configured as alarm func-
tion, and O2FT is set to OFF, then out-
put 2 will go off. Otherwise, output 2
will go on if O2FT is set to ON.