Mantracourt ICA1H, Руководство пользователя

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Mantracourt Electronics Limited – ICA User Manual
13
ICA5S & ICA5A
The ICA5S & ICA5A (2-wire 4 - 20 mA) In-Cell strain gauge amplifiers are supplied un-calibrated but optimized for a
sensitivity of 2.5 mV/V. To accommodate other sensitivities the gain resistor ‘R
gain
’ as shown in Figure 2.10, can be
changed according to the following formulas. Load cells with less than 1 mV/V sensitivity are not recommended due to
the low excitation voltage presented to the load cell by a 2-wire device (see table below).
N.B. a high quality, <=25 ppm/
°C
1 % metal film resistor should be used for optimum performance. It may be
necessary to use an E96 value to optimise the trim range.
Table 3.6 ICA5S & ICA5A (4-20mA) Gain Resistor Formula
 























10
20000
20000
/
6 . 613 Z
Vexc V mV
R
x
k ohms
Where
V mV /
is the sensitivity of the load cell (in mV/V), V
exc
is the excitation voltage (in volts) and Z is the load cell
impedance (in ohms).
e.g. For a 2.5 mV/V 1000 ohm load cell: R2 = 222.17 k ohms – use 220 k (nearest E24 preferred value) or 223k (nearest
E192 preferred value)
The following table gives calculated values of V
exc
for various standard load cell impedances:
Load Cell Impedance Excitation voltage (V
exc
)
350 0.55
700 0.90
1000 1.11
1400 1.32
2000 1.54
5000 1.99
Use the following formulas to calculate the excitation voltage for cell impedances not given in the table:






  

6 exp 10 762 . 4 ) / 1 (
1
Rcell
R
exc
ohms









1240
5 . 2
Rx
Rx
V
exc
volts
e.g. for a 500 ohm load cell:
R
exc
= 498.8 ohms
Excitation voltage, V
exc
= 0.717 V
ICA5S & 5A Offset Resistor (R
offs
)
The value of R
offs
can be changed to offset the zero point if it is outside the normal trimming range (±2% FS).
Its value will also depend on the impedance of the load cell. The factory-fitted value, 180k is optimised for a 1000 ohm
cell.