Siemens UM344-2 user manual Determine Sensor Cable Requirements

UM344-2 INSTALLATION

ŸIndividual miscellaneous hardware must meet the following requirements:

Ÿ Capacitance to Ground	50 pF maximum
Ÿ Resistance to Ground	1 MΩ minimum
Ÿ Impedance if Series Connected	Less than 10Ω
Ÿ Impedance if Parallel Connected	Greater than 50kΩ.

ŸThe maximum number of miscellaneous devices per Network is 16. The combined electrical characteristics may not exceed the following:

Ÿ Maximum capacitance to ground	................ 800 pF
Ÿ Minimum resistance to ground	62.5kΩ
Ÿ Maximum series impedance	160Ω
Ÿ Minimum parallel impedance	3125Ω

4.3.9 Determine Sensor Cable Requirements

If the Transmitter is mounted remotely from the sensor, the wire characteristics of the extension cable between the sensor and Transmitter will be different for thermocouple inputs than for RTD, ohm, or millivolt type inputs.

A.Thermocouple Sensor-to-Transmitter Extension Cable:

1)Select extension grade or thermocouple grade wire of the same calibration as the thermocouple: calibrations are T, J, E, K, R, S, N, B.

∙THERMOCOUPLE GRADE: Wire is made from same materials as thermocouple and subject to same limits of error as thermocouple.

∙EXTENSION GRADE: Noble and refractory thermocouple extension grade wire is made from inexpensive proprietary alloys that simulate the thermoelectric behavior of the actual thermocouple element over a limited range of temperatures.

Base metal (T, J, K, E) thermocouple extension grade wire is made from the same materials as thermocouple wire; however, its use is restricted to a lower range of temperatures.

For extension grade wire, the ambient temperature at the thermocouple head connection point may not exceed the temperature limits of the extension wire.

2)Cable Recommendation: FEP insulated and jacketed, twisted and shielded. Wire size should be 16 to 20 AWG.

September 1995 4-13