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And the internal working value of FFST is reset to 1, being incremented each update set by RATE until it reaches
the user set value of FFST.
Cell
Provides the level where the integration between the DCell/DSC and the strain gauge bridge takes place. Features
include, when the optional temperature module is fitted, 5-point temperature compensation to produce a
temperature compensated value CMVV. Scaling using a gain and offset, CGAI and COFS respectively, producing a
value known as CRAW. Linearisation, using up to 7-points, producing the final output from this section known as
CELL. Over load and under load values can be set in CMIN & CMAX to alert the user of forces less or greater than
the integrator has intended the unit to be operated. These features allow the output CELL to be in force units which
can be used by 'System' to convert to units of weight.
Temperature compensation and Linearisation are covered in detail in their own chapters.
Temperature Compensation In Brief
When the optional temperature hardware module DTEMP is connected the temperature compensation is available.
The temperature compensation facility can remove the need for the fitting of compensation resistors to the strain
gauges. This compensation can apply for gain and offset with up to 5 temperature points.
The input for the temperature compensation is MVV and the output from the process is CMVV. If not temperature
compensation is invoked the CMVV is equal to MVV
A Detailed explanation is given in chapter 5
Cell Scaling, CGAI, COFS
The temperature compensated value CMVV is scaled with gain and offset using CGAI and COFS respectively. The
gain is applied first and the offset then subtracted. This would be used to give a force output in the chosen units,
this output being termed CRAW.
CRAW = (CMVV X CGAI) – COFS
Two Point Calibration Calculations and Examples
Examples are given here for two point calibration, as this is by far the most common method.
Cell Calibration
The scaling parameters are CGAI and COFS
CGAI is in cell-units per mV/V'
COFS is in cell units
The cell output calculation is (in the absence of temperature and linearity corrections) –
CRAW = (CMVV × CGAI) – COFS
If we have two electrical-output (MVV) readings for two known force loads, we can convert the output to the
required range. So if –
test load = fA CMVV reading = cA
test load = fB CMVV reading = cB
– then calculate the following gain value
CGAI = (fB – fA) / (cB – cA)
and the offset is
COFS = (cA x CGAI) – fA
The outputs should then be CELL = fA, fB true force values, as required.
Calibration Methods
There are a number of ways of establishing the correct control values.
Method 1 - Nominal (data sheet) Performance Values
27
Micron Meters
DCell & DSC User Manual
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