Siemens Sitrans, LC 500 instruction manual Interconnection SITRANS LC, Wiring, Supply, Examples

Interconnection: SITRANS LC 500

Wiring

Supply

Notes:

•The transmitter is powered by the current loop and needs at least 9.5-13 Volt on the terminals: 9.5 V at 22 mA or 12 V at 3.6 mA.

•The maximum supply is 33 Volt. If the voltage is higher the device will shut down.

•The loop-circuit will withstand voltages up to 250 Vac/Vdc without any damage.

The SITRANS LC 500 uses a switched power supply circuit, which makes the most efficient use of the available power present on the terminals. If the signal current is low, (4mA), the terminal voltage will be high, and if the signal current is high, (20 mA), the terminal voltage may be low, due to all the resistive elements in the loop, such as the barrier and sense resistor.

Voltage drop versus mA for current transmitter operation

	voltage drop over 250 ohm
	measuring resistance
supply	voltage drop over 280 ohm in
	barrier
	voltage drop over blocking
V-	diode in barrier
	margin or voltage drop over
	instrument cable
	operation voltage,
	transmitter

mA

Examples:

•With a 250 Ohm sensing resistor, no barrier and negligible cable resistance, the overall supply voltage should be at least 15.0 V.

•With a 250 Ohm sensing resistor, a barrier of 280 Ohm, and 20 Ohm cable resistance (500 m), the total resistance is 550 Ohm, so the overall supply voltage should be at least 20.5 Volts.

•For a multi-drop application, where the measuring supply is fixed to 4 mA, the voltage on the terminals of the SITRANS LC 500 should be at least 12 Volts.

The loop circuit is completely isolated from the measurement circuit. It is designed so that the internal capacitance and inductance on the terminals are isolated and do not factor in safety calculations.

Interconnection

7ML19985GE01 SITRANS LC 500 – INSTRUCTION MANUAL Page 23