Siemens Sitrans Grounding instructions, Protection for solid-state switch, Interconnection

Protection for solid-state switch

•For dc circuits: connect protection diodes in the 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 mm2.

•The SITRANS LC 500 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 well1 and/or tank wall, using the ground lug on the housing.

ground lug

label / protective seal

(DO NOT REMOVE)

instrument system ground (connected at factory)

Type:

Ser.:

Date:

Rev.:

Tampering voids warranty

instrument system 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.

7ML19985GE01 SITRANS LC 500 – INSTRUCTION MANUAL Page 27

Interconnection