Super Systems 3 Series - Manual (Page 35)

Series 3 Operations Manual
35
8.2 PV Offset
All ranges of the controller have been calibrated against
traceable reference standards. This means that if the input
type is changed it is not necessary to calibrate the controller.
There may be occasions, however, when you wish to apply
an offset to the standard calibration to take account of
known errors within the process, for example, a known
sensor error or a known error due to the positioning of the
sensor. In these instances it is not advisable to change the
reference (factory) calibration, but to apply a user defined
offset.
PV Offset applies a single offset to the temperature or
process value over the full display range of the controller and
can be adjusted in Level 3. It has the effect of moving the
curve up a down about a central point as shown in the
example below:
8.2.1 Example: To Apply an Offset:
Connect the input of the controller to the source device
which you wish to calibrate to
Set the source to the desired calibration value
The controller will display the current measurement of the
value
If the display is correct, the controller is correctly calibrated
and no further action is necessary. If you wish to offset the
reading:
Do This Display Additional Notes
1. Select Level 3 or
Conf. Then press

to select ‘INPUT’
Scrolling display
‘p r o c e s s i n p u t
l i s t
’
2. Press to
scroll to ‘PV/OFS’
3. Press  or
 to adjust the
offset to the reading
you require
Scrolling display ‘p v
o f f s e t
’
In this case an offset of
2.0 units is applied
It is also possible to apply a two point offset which adjusts
both low and high points. This is done in Level 3 using the
CAL List, and the procedure is described in the Calibration
section 15.
8.3 PV Input Scaling
Input scaling applies to the linear mV input range only. This
is set by configuring the INPUT TYPE parameter to mV and
has an input range of –10 to 80mV. Using an external burden
resistor of 2.49Ω, the controller can be made to accept 4-
20mA from a current source. Scaling of the input will match
the displayed reading to the electrical input levels from the
transducer. PV input scaling can only be adjusted in
Configuration level and is not provided for direct
thermocouple or RTD inputs.
The graph below shows an example of input scaling, where it
is required to display 2.0 when the input is 4mV and 500.0
when the input is 20mV .
If the input exceeds +5% of the mV.Lo or mV.Hi settings,
sensor break will be displayed.
8.3.1 Example: To Scale a Linear Input
Select Configuration level as described in section 6.1.3.
Then:
Do This Display Additional Notes
1. Then press

to select ‘INPUT’
Scrolling display
‘p r o c e s s i n p u t
l i s t
’
2. Press to
scroll to ‘IN.TYP’
3. Press  or
 to ‘mV’
Scrolling display ‘i n p u t
t y p e
’
4. Press to
scroll to ‘MV.HI’
5. Press  or
 to ’20.00’
Scrolling display ‘l i n e a r
i n p u t h i g h
’
6. Press to
scroll to ‘MV.LO’
7. Press  or
 to ‘4.00’
Scrolling display ‘l i n e a r
i n p u t l o w
’
8. Press to
scroll to ‘RHG.HI’
9. Press  or
 to ‘500.0’
In operator level the
controller will read 500.0
for a mV input of 20.00
10. Press to
scroll to ‘RNG.LO’
11. Press  or
 to ‘2.0’
In operator level the
controller will read 2.0 for
a mV input of 4.00
i n p u t
Electrical Input
Display
Reading
Fixed offset
(e.g. 2)
Factory
calibration
2.0
pv.ofs
mv
i n . t yp
20.00
m v. h i
500.0
r h g . h i
4.00
m v. l o
2.0
r h g . l o
For mA inputs
4-20mA = 9.96-49.8mV with
2.49Ω load resistor
0-20mA = 0-49.8mV with
2.49Ω load resistor
mA input will detect sensor
break if mA < 3mA
Use a current source to remove
shunt resistor errors
m v . l o
eg 4 mV
Electrical Input
Display
Reading
R N G . H I
eg 500.0
R n g . l o
eg 2.0
m v . h i
eg 20 mV