Siemens Treadmill LC 500 사용자 설명서

7ML19985GE01

SITRANS LC 500 – INSTRUCTION MANUAL

Page 23

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. 

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.

•

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.

Voltage drop versus mA for current transmitter operation

mA

V-

su

pp

ly

voltage drop over 250 ohm 

measuring resistance

voltage drop over 280 ohm in 

barrier

voltage drop over blocking 

diode in barrier
margin or voltage drop over 

instrument cable

operation voltage, 

transmitter