DESCRIPTION AND OPERATION
MODULE CIRCUITRY
I-E96-302B
2 - 9
baseband communication mode, the input passes through the
baseband communication circuitry for decoding. The micro-
processor coordinates operation of point-to-point input and
output through three sets of multiplexers (analog input, FSK
and baseband).
Figure
shows a typical analog input filter circuit. The cir-
cuit shown in Figure
connects to the FBS termination
(point-to-point) through the P3 connector. Each analog input
has overvoltage protection to protect the FBS 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 FBS 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 FBS mod-
ule stores that value in memory. When in the
point-to-point-mode, the FBS module can input any of these
signal types: four to 20 milliamps, zero to one DC, zero to five
VDC, zero to ten VDC, one to five VDC, or -10 to +10 VDC.
Function code 132 allows selecting the signal type for each
channel.
Communication Circuitry
There are two sets of communication circuitry: one for FSK dig-
ital communication and one for baseband communication. The
mode of communication is selected through an on-board
jumper.
Figure 2-6. Analog Input Filter and Overvoltage Protection
TO ADC
MULTIPLEXERS
LOW PASS
FILTERS
OVERVOLTAGE
PROTECTION (±30 VDC)
ANALOG INPUT
FROM FIELD
ACOM
+
–
TP25180A
