Calibration to Another Instrument (continued)
To make a correction when there are different errors across the scale.
2 Adjust using the SPAN function
2.1Chose a temperature near the bottom and another near the top of the scale.
2.2Run the process at the lower temperature (T1). Note the error (E1) between the controller and the instrument readings.
2.3Repeat at the upper temperature (T2) and note error (E2).
2.4Substitute the values for T1, T2, E1 and E2 in the
expression below to calculate | SPAN | ||||||
|
|
| |||||
|
|
|
|
|
|
| |
For hi.SC settings see level 2. |
|
| |||||
Example: |
| T1 | T2 | ||||
Instrument reading | 58° |
|
| 385° |
| ||
Controller reading |
| 60° |
|
| 400° |
| |
Error |
| E2 | |||||
|
|
|
|
|
|
|
|
385 - 58 |
| 327 |
|
|
|
| |
2.5 Therefore adjust SPAn to
Notes: (1) After making the adjustment the reading will immediately change. Allow time for the temperature to stabilise at T2 before making any further adjustment. At this point, a ZEro adjustment may be needed, refer to step 1 above.
(2)Check that the temperature correctly stabilises at T2 and then adjust setpoints to T1. If an error is present at T1 repeat from step 2.
LINEAR INPUT CALIBRATION
In addition to the ten temperature inputs, the controller has five linear input ranges which can be calibrated to display a range of engineering units. This procedure involves making adjustments to the controller’s hi.SC, ZEro and SPAn adjustments found in function menu levels 2 and 3.
Note: The controllers linear inputs are in mV. If your transducer provides an output in mA this should be converted to mV by feeding the controller input via a high stability one ohm resistor, see figure page 26. Other low Vdc signals can be connected via a suitable voltage divider network to match the controller input requirements.
A d v a n c e d S e t t i n g s
25
