Division 2 Application Example Using Load Cells - Mettler Toledo IND560 Serie Guia De Instalacion

Division 2 Application Example Using Load
Cells
Note: There are many
methods that may be used to
install properly approved
equipment within hazardous
areas. In our example, the
field circuit characteristics
(electrical approval data)
were compared to those of
the load cells connected to
make sure the combination is
safe. In other applications
(specifically in Europe), only
a confirmation of a certain IP
rating and maximum surface
temperature may be required
to connect the devices.
IND560xx Terminal Division 2 and Zone 2/22 Installation Manual
The following is an example of applying the IND560xx terminal in a Division 2
application connecting a model 2158 Vertex floor scale with 50 feet of load cell
cable. The field circuit parameters for all devices and cables in the load cell line
(including the load cells and junction box) must also be known.
Terminal model: IND560xx terminal (Division 2 approved)
Base model: 2158 VERTEX
Load cell model: METTLER TOLEDO 0745A
Quantity of load cells: 4
Load cell cable length: 50 feet
Junction box PCB p/n: 13640300A
IND560xx load cell field circuit parameters from control drawing 72186884CR:
V / U
oc
I / I
sc
C
a
L / L
a
Load cell field circuit parameters from model 745A load cell control drawing:
V
max
I
max
L
Default load cell cable values from IND560xx terminal control drawing
72186884CR:
C
cable
L
cable
The 2158 junction box PCB was determined to not have significant capacitance or
inductance impact. Values shown below should be used.
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
®
(with approved cells)
= 10.0 VDC
o
= 313 mA
o
/ C = 1 µF
o
= 0.6 mH
o
= 25 VDC
= 600 mA
C = 0 µF
i
= 29 µH
i
= 60 pF / foot
= 0.2 µH / foot
C = 0 pF
i
L = 0 µH
i
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