Emerson Rosemount 848T, Справочное руководство, Страница: 17 / 136

9
Reference Manual
00809-0100-4697, Rev GA
Section 2: Installation
November 2014
Installation
Figure 2-5. Sensor Wiring Diagram
A. 2-wire RTD and ohms
B. 3-wire RTD and ohms (Emerson provides 4-wire sensors for all single-element RTDs; use these RTDs in 3-wire
configurations by clipping the fourth lead or leaving it disconnected and insulated with electrical tape.)
C. Thermocouples/ohms and Millivolts
D. 2-wire RTD with compensation loop (transmitter must be configured for a 3-wire RTD in order to recognize an RTD
with a compensation loop)
RTD or ohm inputs
Various RTD configurations, including 2-wire and 3-wire are used in industrial applications. If the
transmitter is mounted remotely from a 3-wire RTD, it will operate within specifications,
without recalibration, for lead wire resistances of up to 60 ohms per lead (equivalent to 6,000
feet of 20 AWG wire). If using a 2-wire RTD, both RTD leads are in series with the sensor element,
so errors can occur if the lead lengths exceed one foot of 20 AWG wire. Compensation for this
error is provided when using 3-wire RTDs.
Thermocouple or millivolt inputs
Use appropriate thermocouple extension wire to connect the thermocouple to the transmitter.
Make connections for millivolt inputs using copper wire. Use shielding for long runs of wire.
Analog inputs
The analog connector converts the 4–20 mA signal to a 20–100 mV signal that can be read by
the 848T and transmitted using F
OUNDATION
fieldbus.
Use the following steps when installing the 848T with the analog connector:
1. The 848T, when ordered with option code S002, comes with four analog connectors.
Replace the standard connector with the analog connector on the desired channels.
2. Wire one or two analog transmitters to the analog connector according to Figure 2-6 .
There is space available on the analog connector label for identification of the analog
inputs.
Note
Power supply should be rated to support the connected transmitter(s).
3. If the analog transmitters can communicate using HART
®
protocol, the analog
connectors are supplied with the ability to switch in a 250 ohm resistor for HART
communication (see
Figure 2-7 ).
One switch is supplied for each input (top switch for “A” inputs and bottom switch for
“B” inputs). Setting the switch in the “ON” position (to the right) bypasses the 250 ohm
resistor. Terminals are provided for each analog input to connect a field communicator
for local configuration.
1 2 3
A
B
C
1 2 3 1 2 3
D
1 2 3