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4-4
Chapter 4 Electrical Wiring
„
Hollow Cable (Between the Probe and Junction Box)
Use the special cable in the hollow pipe (hollow cable) connected at the time of shipment
for wiring. Do not use any other wire or cable. Additionally, since the wiring of this section
was done at the factory, please use it as it is.
„
Grounding
Grounding is very important to prevent the device from being damaged by induced light-
ning surge. Be sure to do the grounding work.
y
Ground the device with a resistance of less than 100 Ω. In a location where large
induced lightning surge can be expected or frequently occurs, use more advanced
grounding. This will ensure the sufficient performance of the built-in lighting arrestor.
y
Use 600 V PVC-insulated wires for grounding.
y
Probe
The probe does not need to be individually grounded because grounding the junction box
grounds the probe.
y
Junction box
y
Be sure to ground the junction box, since doing so effectively grounds the probe.
y
Ground terminals are located both on the inside (GND part of the terminal plate) and
outside (case) of the junction box. Either terminal can be used.
„
Power Supply and External Load Resistance
It is necessary to determine the relationship between the power voltage and external load
resistance used for this device within the range shown in the figure below. The external
load resistance is the sum total of the resistance values connected to the output terminals
of this device, such as the resistance of the cables that make up the loop and the internal
resistance of connected gauges.
Supply voltage E (V DC)
Normal
operating range
12.5 35 17.9
245
1026
0.02193
E−12.5
R
Lo
ad r
esi
sta
nce R (Ω)
Fig. 4-4. Relationship between the power supply and external load resistance