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Protection for solid-state switch
•
For dc circuits: connect protection diodes in the correct polarity across the relay
coil.
•
For ac circuits: connect a Voltage Dependent Resistor (VDR) or other ac compatible
component (such as zeners and protection diodes in combination) in the correct
polarity across the relay coil.
Grounding instructions
Notes:
•
Since the measurement occurs between the Measurement and Ground
connections, it is important to have good, low-resistance, reliable connections in
this circuit.
•
Use a ground connection wire with a sufficiently large diameter relative to its
length, and not less than 1 mm
•
The SITRANS LC500 measurement circuit is completely isolated from the loop
circuitry: this allows either line of the loop circuit to be grounded if requirements
for Ex safety are followed and if the power supply voltage is less than 33 Vdc.
Connect the housing and the process connection with either the stilling well
wall, using the ground lug on the housing.
instrument system ground
(connected at factory)
ground connection point
WARNING: When connecting the probe, do not leave moisture or metal scrap
(from the cable shielding, for example) inside the housing. This could interfere
with transmitter operation, or cause a short circuit.
1.
Where the stilling well is welded to the tank.
Page 30
SITRANS LC500 – OPERATING INSTRUCTIONS
2
.
instrument system
1
and/or tank
ground lug
label / protective seal
(DO NOT REMOVE)
7ML19985GE04
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