Mantracourt Electronics Limited
DCell & DSC MantraCAN User Manual
32
STAT
, the value of
CRAW
is also clamped to this value. On
CRAW
being less than the value set in
CMIN
the
CRAWUR
flag is set in both
FLAG
and
STAT
, the value of
CRAW
is also clamped to this value.
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
.
Linearisation cannot be used at RATE of 8 (200Hz)
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 :
CELL reading cA = 100.0112
For test load of xB = 500.07Kg:
CELL reading cB = 498.7735
