Sensor Connections; Thermocouple Or Millivolts Inputs; Rtd Or Ohm Inputs - Emerson Rosemount 648 Reference Manual

Configuration
July 2016
Electrical shock can result in death or serious injury.
Avoid contact with the leads and terminals. High voltage that may be present on

leads can cause electrical shock.
This device complies with Part 15 of the FCC Rules. Operation is subject to the
following conditions:
This device may not cause harmful interference.

This device must accept any interference received, including interference that

may cause undesired operation.
This device must be installed to ensure a minimum antenna separation distance

of 20 cm from all persons.
The power module may be replaced in a hazardous area. The power module has surface
resistivity greater than one gigaohm and must be properly installed in the wireless
device enclosure. Care must be taken during transportation to and from the point of
installation to prevent electrostatic charge build-up.
2.3

Sensor connections

The Rosemount 648 Wireless is compatible with a number of RTD and thermocouple sensor
types. Figure 2-1
transmitter. To ensure a proper sensor connection, anchor the sensor lead wires into the
appropriate compression terminals and tighten the screws.
Make sensor connections through the cable entry in the side of the connection head. Be
sure to provide adequate clearance for cover removal.
When using Rosemount X-well
assembled to a Rosemount 0085 Pipe Clamp RTD Sensor in a direct mount 3-wire
configuration.
2.3.1

Thermocouple or millivolts inputs

The thermocouple can be connected directly to the transmitter. Use appropriate
thermocouple extension wire if mounting the transmitter remotely from the sensor.
2.3.2

RTD or ohm inputs

The Rosemount 648 Wireless will accept a variety of RTD or ohmic configurations, including
2-, 3-, or 4-wire connections. If the Rosemount 648 Wireless is mounted remotely using a 3-
or 4-wire connection, it will operate withing specifications without recalibration for lead
wire resistances of up to 5 ohms per lead (equivalent to 500 ft. of 20 AWG wire). In this case,
the leads between the RTD and transmitter is recommended to be shielded.
If using a 2-wire connection, both RTD leads are in series with the sensor element. This can
cause significant errors if the lead lengths exceed 3 ft. of 20 AWG wire (approximately
0.05 °C/ft.). For longer runs, it is recommended to attach a third or fourth lead to achieve
the benefits of a 3- or 4-wire connection as described above.
4
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shows the correct input connections to the sensor terminals on the
™
Technology, the Rosemount 648 Wireless is required to be
Reference Manual
00809-0200-4648, Rev BB
Configuration