Mettler Toledo PANTHER Guia De Instalacion página 199

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 (but not inductance) of the load cell must be multiplied by the quantity of load
cells used. Also, the field circuit parameters for the load cell cable must be multiplied by the
total load cell cable length.
Formula
must be ≥ V
V
max t
25 VDC ≥ 5.5 VDC
must be ≥ I
I
max t
600 mA ≥ 166 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 = 3 nF
cable
(0 µF + 0 µF + 3 nF) ≤ 590 µF
≤ L
L + L
i cable a
L = 29 µH (the largest inductance value of a single cell is used)
i
L = 0 µH (junction box)
i
L = 0.2 µH / foot * 50 feet = 10 µH
cable
(29 µH + 0 µH + 10 µH) ≤ 1.3 mH
In addition to the formulas above, the temperature rating of the PANTHER panel-mount
terminal must be checked against the AIT (Auto Ignition Temperature) of the hazardous
product. For this example, the hazardous product has an AIT of 200°C (393°F) which is
higher than the rating of the panel-mount terminal, which is 120°C (248°F). This indicates
the temperature comparison test passes.
Since all four field circuit parameters compare favorably and pass the formula evaluation
and the temperature comparison test passes, the products listed in this example may be
safely installed into a Division 2 area. They must be installed according to control drawing
155907R using all pertinent local and national standards. Note that the load cells must
also be approved for use in Division 2 areas and the field circuit parameters and
temperature ratings must be known. If the load cells used (regardless of manufacturer) do
not have Division 2 approval, they cannot be connected to the PANTHER panel-mount
terminal in an area classified as Division 2.
Chapter 2: Installation
Application Example Using Load Cells
Pass or Fail
PASS
PASS
PASS
PASS
(7/03) 2-5