Mettler Toledo Division 2 IND570 Serie Guia De Instalacion página 22

IND570xx load cell NIFW parameters from control drawing 30116036:
Load cell NIFW parameters from model 745A load cell control drawing:
Default load cell cable values from IND570xx terminal control drawing 30116036:
The 2158 junction box PCB falls into the "simple" device category which means it has no active to
store energy. For US/Canada, this means it can be ignored in the NIFW calculations. For ATEX
applications, the junction box must be evaluated and approved – even if it includes no active
components. There will be maximum voltage and current limits which have to be evaluated and
possibly a small amount of capacitance and/or inductance that must be added to the calculation.
These ATEX calculations are not shown here.
Now, compare these values using the formulas provided in the previous section of this chapter and
determine if all four criteria pass or fail. Note that the field circuit parameters for capacitance of the
load cell must be multiplied by the quantity of load cells used. The inductance value is the same for
1 through 8 load cells. Also note that the field circuit parameters for the load cell cable must be
multiplied by the total load cell cable length.
30205321 | 02 | 05/2017
V / U = 10.5 VDC
oc o
I / I = 304 mA
sc o
C / C = 1 µF
a o
L / L = 0.6 mH
a o
V = 25 VDC
max
I = 600 mA
max
C = 0 µF
i
L = 29 µH
i
C = 60 pF / foot
cable
L = 0.2 µH / foot
cable
U / V must be ≥ U / V
i max o oc
12 VDC ≥ 10.5 VDC
I / I must be ≥ I / I
i max o sc
600 mA ≥ 304 mA
≤ C
C + C
i cable a
C = 0 µF * 4 cells = 0 µF (load cells)
i
C = 0 µF (junction box)
i
C = 60 pF / foot * 50 feet = 3000pF = 0.003 µF
cable
(0 µF + 0 µF + 0.003 µF) ≤ 1 µF
METTLER TOLEDO IND570xx Division 2 and Zone 22 Installation Manual
Formula Pass or Fail
PASS
PASS
PASS
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