Reference Manual
00809-0100-4697, Rev EA
October 2011
2-5
Rosemount 848T
RTD or Ohm Inputs
Various RTD con figurations, includ ing 2-wire and 3- wire are used in industr ial
applications. If the transmitter is mounted remotely from a 3-wire RTD, it will
operate within specifications, without r ecalibration, for lead wire resist ances 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 e xceed one fo ot of 20 AWG wire. Compensation
for this error is provided when using 3-wire RTDs.
Thermocouple or Millivolt Inputs
Use appropriate thermo couple extension wire to conn ect 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 FOUNDATION 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 analo g
connectors. Replace the standard connector with the analog connector
on the desired channe ls.
2. Wire one or two an alog transmitters to the a nalog connector according to
Figure 2-5. 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 HAR T communication (see Figure 2-6).
One switch is supplied for each input (top switch for “A” inputs and
bottom switch for “B” inputs). Setting the switc h in the “ON” position (to
the right) byp asses the 250 ohm resistor . Terminals are provided fo r each
analog input to connect a Field Communicator for local configuration.