Instruction manual

7
MODEL XMT-P pH/ORP SECTION 1.0
DESCRIPTION AND SPECIFICATIONS
1.7 FOUNDATION FIELDBUS
Figure 1-3 shows a Xmt-P-FF being used to measure and control pH and chlorine levels in drinking water. The figure also
shows three ways in which Fieldbus communication can be used to read process variables and configure the transmitter.
FIGURE 1-3. CONFIGURING MODEL XMT-P TRANSMITTER WITH FOUNDATION FIELDBUS
1.6 HART COMMUNICATIONS
1.6.1 OVERVIEW OF HART COMMUNICATION
HART (highway addressable remote transducer) is a digital communication system in which two frequencies are superim-
posed on the 4 to 20 mA output signal from the transmitter. A 1200 Hz sine wave represents the digit 1, and a 2400 Hz
sine wave represents the digit 0. Because the average value of a sine wave is zero, the digital signal adds no dc compo-
nent to the analog signal. HART permits digital communication while retaining the analog signal for process control.
The HART protocol, originally developed by Fisher-Rosemount, is now overseen by the independent HART
Communication Foundation. The Foundation ensures that all HART devices can communicate with one another. For more
information about HART communications, call the HART Communication Foundation at [phone]. The internet
address is http://www.hartcomm.org.
1.6.2 HART INTERFACE DEVICES
The Model 375 HART Communicator is a hand-held device that provides a common link to all HART SMART instru-
ments and allows access to AMS (Asset Management Solutions). Use the HART communicator to set up and control the
Xmt-P-HT and to read measured variables. Press ON to display the on-line menu. All setup menus are available through
this menu.
HART communicators allow the user to view measurement data (pH, ORP and temperature), program the transmitter, and
download information from the transmitter for transfer to a computer for analysis. Downloaded information can also be sent
to another HART transmitter. Either a hand-held communicator, such as the Rosemount Model 375, or a computer can be
used. HART interface devices operate from any wiring termination point in the 4 - 20 mA loop. A minimum load of 250 ohms
must be present between the transmitter and the power supply. See Figure 1-4.
If your communicator does not recognize the Model XMT pH/ORP transmitter, the device description library may need
updating. Call the manufacturer of your HART communication device for updates.
Xmt-P-FF