Connection Technology Center, Inc.
590 Fishers Station Drive
Victor, New York 14564
Toll Free: (800) 999-5290
Phone: (585) 924-5900
Fax: (585) 924-4680
2 Wire 4-20mA Sensor and 4 Wire Transmitter Application Note
2 Wire 4-20mA Sensors
2 Wire Loop Power sensors from CTC require
only 2 connections, a +18 to 30 Volt Power lead
and a DC common (negative) lead. The sensor
regulates the loop so that the current is
proportional to the vibration parameter being
measured.
PLC Input Module or
Process Controller
+V
Loop Powered Sensor
+
+
GND
Power
Supply
Measurement
Electronics
4-20 mA
Input 1
Figure 1
Figure 2 shows an example of a Loop Powered
Sensor’s Output vs. Time.
Loop Power Output
Velocity (inches/second peak)
The sensors can be wired directly into analog
input modules on PLC’s or Process Controllers
that accept 4 – 20 mA signals. The sensor must
be connected to a power source at the positive
lead and the common (negative) lead will be
connected to the Controller’s Analog Input. The
power supply is used to complete the loop
through the Controllers Ground. See figure 1.
0.6
Alarm
0.5
Alert
0.4
0.3
0.2
0.1
0
0:00:00
12:00:00
24:00:00
36:00:00
Time (hours)
Figure 2
48:00:00
60:00:00
4 Wire 4-20 mA Transmitters
Continuous 4-20 mA Output
V e lo c ity (in c h e s /s e c o n d p e a k )
CTC’s Vibration Transmitters constitute a more
versatile approach to continuous monitoring
than the standard Loop powered sensors. The
transmitters are capable of wider frequency and
amplitude ranges and can provide a dynamic
vibration signal in addition to the overall 4-20
mA output. The dynamic vibration signal is
available through a buffered output. Figure 3
shows an example of the dual outputs of CTC’s
Vibration Transmitter.
0.6
0.5
0.4
0.3
0.2
0.1
0
0:00:00
12:00:00
24:00:00
36:00:00
Time (hours)
The 4 wires needed to monitor overall vibration
level using a transmitter are the Positive and
Negative Power Supply leads that will provide
power to the electronics, and the Positive and
Negative Output SIGNAL leads. These 2 pairs
of leads are separate and distinct from one
another. Figure 4 shows typical wiring into a
PLC or Process controller with analog input
module.
Figure 3
A 2 conductor cable with a Plug (F) type BNC
Connector can be used to monitor the dynamic
vibration signal coming out of the BNC Jack on
the Transmitter.
Figure 4
Transmitter
Sensor
Input
4 – 20 mA
IN +
+
+
Measurement
Electronics
Output
-
IN -
- + -
+
Power
Supply
Dynamic
Signal Output
PLC Input Module
or Process
Controller
48:00:00
60:00:00