THEORY OF OPERATION
FCS MODULE CIRCUITRY
I-E96-314A
2 - 5
Figure
is a typical example of a sinusoidal input signal
(E1). Diodes CR4-CR7 clip the input signal at +10 V limiting
the input amplitude to 20 Vp-p (E2). R4 through R7 limit the
inrush current. This circuit can process input signals that
range from 300 mVp-p to 120 Vrms at frequencies in the range
of 1 Hz to 12.5 KHz.
The comparator works as a zero crossing circuit. It converts
the input signal to a digital waveform (E3). A high frequency fil-
ter (R4,R5,C3) removes noise from the input signal before
reaching the comparator (operational amplifier).
The NAND gate provides gating for the input enable function.
No input signal can pass until the MCU is ready to count and
process data from the field.
Microcontroller
The microcontroller (MCU) is responsible for collecting data,
timing the data and communicating with the MFP. Residing in
the MCU is the firmware that directs the FCS operation. The
MCU counts pulses at the interrupt level. When the MCU inter-
rupt is ready to receive input pulses, it enables an input gate to
allow data to pass. An internal program in the MCU compiles
the count and formats it for the processor module. The MCU
sends the count and timer information to the double buffered
storage area.
Data from the MCU goes to the first set of buffered latches. A
data request from the MFP transfers data from the buffered
latches to the slave expander bus interface.
Figure 2-3. Input Signal Conditioning Circuit
TP25012A
P3 1
P3 A
PIN
NIN
R4
R5
R6
R7
R10
R11
5 V
CR5
CR6
R8
R9
CR4
CR7
C3
A
2
3
7
5
6
1
11
12
13
1
2
LM311
74HC14
74HC00
-10 V
+10 V
+10 V
-10 V
300 mV P-P AT
3 Hz NIM
120 VAC MAX
INPUT
ENABLE
E1
E2
E3
–
+
U18
U3
U4
P
