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Scale and Offset (User-Defined Scaling)
User-Defined Scaling in the MDCL is provided for converting Modbus readings to physical values such
as temperature, pressure, flow, acceleration, and position. It is useful for users to recode, analyze
and present data with engineering units. Scaling can be accomplished by applying scale factor (slope)
and offset (y intercept) for one channel in record.csv.
The following formula is used to calculate scaling:
Actual value = Modbus Reading * Scale +Offset
The scale (slope) is the rise over the run; that is, how much the line rises vertically compared with
how much it runs horizontally. Here we use two given points to calculate the slope and offset.
Example 1: Converting reading of K type thermocouple from the M-7018 into degrees Celsius
Input type: K type thermocouple (0F)
Data Format
Modbus Reading
Actual Temperature
High
13720
1372°C
Low
-2700
-270°C
Scale
=
Offset = Actual value - Modbus Reading * Scale
= 1372 – (13720 * 0.1)
= 0
=
13720 – (-2700)
1372 – (-270)
= 0.1
(y2- y1)
(x2 –x1)
(Reading
High
- Reading
Low
)
(
Actual
High
- Actual
Low
)
=
=
∆
y
∆
x
Modbus Reading
Actual Temperature
(13720, 1372)
(-2700, -270)
∆
y
∆
x