Siemens Treadmill LC 500 사용자 설명서

7ML19985GE01

SITRANS LC 500 – INSTRUCTION MANUAL

Page 25

2.

Calculate the length of cable allowed, by subtracting the capacitance value that the 

device presents on the loop from the total capacitance. SITRANS LC 500 has no 
measurable capacitance value, but assume 5 nF. Then use the maximum capacitance 
limit (1 m /10 nF) to determine the cable length.

 nF

 m

In an IS application, the IS side of the barrier allows for only 70 nF. 

Example:

Subtract the capacitance for the device:

nF

 m

This allows for a maximum 650 meters on the IS side. 

On the other side of the barrier:

 nF

which allows for 560 meters on that side.

In IIB type/class hazardous area applications the maximum allowed capacitance value is 
330 nF, as long as you are not using HART. If you are using HART, the maximum cable 
length will be limited. Depending on cable specifications, the maximum length lies 
between 1 and 3 km. 

In a multi-drop application, the total capacitance of all the devices must be calculated. 
With five devices, at 5 * 5 nF, the allowable cable length will be considerably limited.

The resistance of this length, 650 + 560 meters, could reach 145 Ohm (at 

120 Ohm / km), which is too much. In this case, use a thicker cable with lower 
resistance. 

•

If the device is part of a multi-drop setup, the SITRANS LC 500 sets the current to 
4 mA, which inhibits analog signalling, including fault signalling.

•

Multi-drop is a HART mode where devices are set to a fixed current, and the 
device is interrogated periodically. The maximum number of devices on one loop 
is 15, one of which can be an analog mode device.

121 5

116

=

–

116 10

1160

=

×

70 5

65

=

–

65 10

×

650

=

121 65

56

=

–