Ica5S & Ica5A; Ica5S & 5A Offset Resistor (R ) - Mantracourt ICA1H User Manual

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
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

 
613 6 .
    

R

x
 

mV / V Vexc
Where is the sensitivity of the load cell (in mV/V), V
mV / V
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
Load Cell Impedance
350
700
1000
1400
2000
5000
Use the following formulas to calculate the excitation voltage for cell impedances not given in the table:

1
  
R

exc

( / 1 Rcell ) . 4 762

 
2 5 . Rx
volts

 
V

exc
 
Rx 1240
e.g. for a 500 ohm load cell:
R = 498.8 ohms
exc
Excitation voltage, V = 0.717 V
exc
ICA5S & 5A Offset Resistor (R
The value of R can be changed to offset the zero point if it is outside the normal trimming range (±2% FS).
offs
Its value will also depend on the impedance of the load cell. The factory-fitted value, 180k is optimised for a 1000 ohm
cell.
13
Mantracourt Electronics Limited – ICA User Manual
 
 
 
Z 20000
  
 
10
k ohms
 

20000
exc
Excitation voltage (V
0.55
0.90
1.11
1.32
1.54
1.99

ohms
 
 

10 exp 6
)
offs
is the excitation voltage (in volts) and Z is the load cell
exc
for various standard load cell impedances:
)
exc
' as shown in Figure 2.10, can be
gain