2 System description
266 MODBUS® multivariable transmitter User manual 2105216 Rev. AB | 3
2 System description
Introduction
The 266 multivariable transmitter is a modular device that provides live readings of differential pressure (DP), static pressure
(SP), and temperature (Tf) via MODBUS
®
protocol to a Host device. Configuration and the display of readings is provided by the
LCD assembly located in the front of the unit. Access to wiring terminations is provided by a terminal block located in the rear of
the transmitter.
Theory of operation
This intelligent multivariable transmitter provides precise and reliable measurement of static pressure, differential pressure, and
process temperature (from an external RTD) once every second. The differential pressure measuring ranges are scaled from
6.2 to 1993 mbar (2.5 to 800 inH
2
O). The measuring ranges for static pressure are 0 to 210 bar (0 to 3046 PSI). The unit
transmits a digital output signal utilizing RTU MODBUS
®
communication protocol and is able to co-exist with an existing ABB
267/269CS multivariable transmitter on the same RS-485 communications bus.
The following graphic demonstrates the live inputs of differential pressure (DP), static pressure (SP) and temperature (Tf) for the
266 transmitter (Figure 1). All three of these input values are derived from the measurement stream: two through the transmitter
pressure taps connected to the stream, and the flowing temperature as measured by the RTD.
Where:
DP = Differential Pressure
SP = Static Pressure
Tf = Flowing Temperature
Figure 1: 266 Multivariable transmitter and RTD process inputs
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