Linearisation In Brief; System; System Scaling, Sgai, Sofs - Mantracourt DSC User Manual

Linearisation In Brief

Linearisation allows for any non-linearity in the strain gauge measurement to be removed. Up to 7 points can be set
using CLN. The principle of operation is that the table holds a value at which an offset is added. The point in the
table that refer to CRAW are named CLX1..CLX7. The offsets added at these point are named CLK1.. CLK7 and are
set in thousandths of a cell unit. The output from the Linearisation function is CELL. If no Linearisation is used (CLN
< 2) the CELL is equal to CRAW.
A Detailed explanation is given in chapter 6

System

System is where the "Force" output, CELL, is converted to weight when installed into a system. Other features such
as SZ offers a means of zeroing the system output SYS. Peak and Trough values are also recorded against the value
of SYS, these are volatile and reset on power up. A command SNAP records the next SYS value and stores in SYSN,
this is useful where more than 1 device in a system and to prevent measurement skew across the system the SNAP
command can be broadcast to all devices ready for polling of their individual SYSN values.

System Scaling, SGAI, SOFS

The cell output value CELL is scaled with gain and offset using SGAI and SOFS respectively. The gain is applied first and the offset the
subtracted. This would be used to give a force output in the chosen units, this output being termed SRAW.
SRAW = (CELL X SGAI) – SOFS
If we have two cell-output (CELL) readings for two known test loads, we can convert the output to the required
range. So if –
Test load = xA  CELL reading = cA
Test load = xB  CELL reading = cB
Then we calculate the following gain value
SGAI = (xB – xA) / (cB – cA)
And then the offset
SOFS = (cA x SGAI) - xA
The outputs should now be SRAW = xA, xB true load values, as required.
Example of calculations for SGAI and SOFS
Example:
A 2500Kgf load cell installation is to be calibrated by means of test weights.
The cell calibration gives an output in Kgf ranging 0–2000.
A system calibration is required to give an output reading in the range 0–1.0 tonnes.
Calculations
Take readings with two known applied loads, such as –
For test load of xA = 99.88Kg :
For test load of xB = 500.07Kg:
Calculate gain value. In this case put SGAI = (xB – xA) / (cB – cA)
= (0.50007 – 0.09988) / (498.7735 – 100.0112)
≈ 0.001003580 = 1.003580x10
29 Micron Meters
CELL reading cA = 100.0112
CELL reading cB = 498.7735
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DCell & DSC User Manual