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3.9
User Calibration
Each unit is calibrated in the factory before shipment. The user can still modify the calibration in the field.
The basic calibration of the controller is highly stable and set for life. User calibration allows the user to offset
the permanent factory calibration in order to:
v
Calibrate the controller to meet a user reference standard.
v
Match the calibration of the controller to that of a particular transducer or sensor input.
v
Calibrate the controller to suit the characteristics of a particular installation.
v
Remove long term drift in the factory set calibration.
There are two parameters: Offset Low (OFTL) and Offset High (OFTH) for adjustment to correct an error in
the process value.
There are two parameters for the sensor input. These two signal values are CALO and CAHI. The input
signal low and high values are to be entered in the CALO and CAHI parameters respectively.
Refer to
section 1.6
for key operation and
section 1.7
for the operation flowchart. Press and hold the
key
until the setup Menu page is obtained. Then, press and release the
key to navigate to the calibration low
parameter OFTL. Send your low signal to the sensor input of the controller, then press and release the
key. If the process value (the upper display) is different from the input signal, the user can use
and
keys to change the OFTL value (the lower display) until the process value is equal to the value the user
needs. Press and hold the
key for 5 seconds to complete the low point calibration. A similar procedure is
applied for high scale calibration.
As shown below, the two points OFTL and OFTH construct a straight line. For the purpose of
accuracy, it is best to calibrate with the two points as far apart as possible. After the user calibration is
complete, the input type will be stored in the memory. If the input type is changed, a calibration error will
occur and an error code
is displayed.
3.10
Digital Filter
In certain applications, the process value is too unstable to be read due to electrical noise or interference. To
improve this, a programmable filter in the controller can be used by setting the “FILT” parameter. A value of
0.5 seconds is used as a factory default. Adjust FILT to change the time constant from 0 to 60 seconds. 0
seconds represents no filter applied to the input signal. The filter is characterized by the following diagram.
