DESCRIPTION AND OPERATION
FUNCTIONAL OPERATION
2 - 4
WBPEEUI240756A0
®
handles FSK digital signals when the IMFEC11 module is in
the field bus mode. On-board jumpers on the IMFEC11 set the
operating mode.
NOTE: In field bus mode, the IMFEC11 module can handle up to 15
transmitters. The Type STT03 terminal can program a maximum of
eight transmitters on a single field bus. Refer to the
mitter Terminal, Type STT03 instruction for more information
(Table
ANALOG INPUTS (POINT-TO-POINT MODE)
All analog inputs are point-to-point. Each channel has an ana-
log input filter that separates the communication signal from
the process data (analog input) before the data goes to the ana-
log-to-digital converter (ADC). In the FSK communication mode
(IMFEC11), the FSK digital communication signal rides on a
small portion of the analog input signal. That input also passes
through the FSK communication circuitry for decoding. The
microprocessor coordinates operation of point-to-point input
and output through multiplexers.
Figure
shows a typical analog input filter circuit. The cir-
cuit connects to the FEC termination (point-to-point) through
the P3 connector. Each analog input has overvoltage protection
to protect the circuitry. The analog signal passes through two
low pass filters that separate communication from data. The
microprocessor multiplexes the filtered input signal (process
data) to the ADC circuitry for conversion.
The FEC module does analog-to-digital conversions on each
input channel continuously at five times per second. After con-
verting the analog signal to a digital equivalent, the FEC mod-
ule stores that value in memory. When in the
point-to-point-mode, the FEC module can input four to 20 mil-
liamps or -10 to +10 VDC. Function code 132 allows selecting
the signal type for each channel.
Figure 2-2. Analog Input Filter and Overvoltage Protection
TO ADC
MULTIPLEXERS
LOW PASS
FILTERS
OVERVOLTAGE
PROTECTION (±30 VDC)
ANALOG INPUT
FROM FIELD
ACOM
+
–
TP25180A
