Instruction Manual
Tek-LCD 7801C
www.tek-trol.com
Technology Solutions
22
Fig 10:
3-
Wire Transmitters Powered Externally
4.2.5
Flow Meter Pulse Input Connections
•
Flow Meter Pulse Inputs are wired to four
-terminal connectors (two inputs per connector).
•
A square waveform is used in the illustration, but the pulse input can read many types of
signals within the specified voltage and frequency ranges.
Fig 11: Flo
w Meter Pulse Input Connections
4.2.6
Digital Input Connections
•
Inputs are wired between terminals 1-5 of the digital input connector and the G terminal of
the 2-position connector above the digital inputs.
•
Normally open switch contacts can be used as shown in
Figure 1
2. The diagram also shows a
Digital Input using an NPN open collector transistor output from a live signal. Logic LO or
switch closure appearing across the terminals is interpreted as ON. When using an open
collector transistor, a logic HI at the
base (marked “B” in Figure 1
2) will be interpreted as ON.
•
The 2-
position connector has a +5 V terminal that can be used to provide excitation to some
sensors requiring more than the pull-up provided on each digital input terminal.
Fig 12:
Digital Input from Switch Closure and Live Signal
S- S+
Pulse Input
+
-
Signal Source
G
Digital Inputs
+5V
1
2
3
4
5
Switch
Contact
Live
Signa l
C
E
B
mA- mA+ 24V
3-Wire 4-20 mA
Transmitter
Analog Input
+
External
Power Supply
Power +
Signal -
-
