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In this video, we're going to show you
how to wire a few different transducers and transmitters
to digital and analog PLC input modules.
We’re also going to analyze a typical instrument field-wiring drawing
to show you how PLCs are properly configured
for different transducer and transmitter types.
The terms transducer and transmitter have become confusing
because they are used interchangeably by different people.
In particular, the term transducer is tossed around as a name
for many devices and instruments.
Just for clarity,
let’s look at the differences between a Transducer and a Transmitter.
A transducer is a device that converts one form of energy
to an electrical or electronic signal.
A Pressure switch is a two-part device consisting of a sensing transducer
and an electrical switch.
A pressure switch is a digital device
because it has only two possible conditions – open or closed.
It is therefore connected to a PLC digital input module.
A Pressure Transmitter is a two-part device consisting of a sensing transducer
and a circuit that transmits a standard instrumentation electrical signal
representing a physical variable being measured.
In most applications, the electrical signal is 4 to 20 milliamps.
A Pressure Transmitter is an analog device
and is therefore connected to a PLC analog input module.
Many people refer to this device as a Transducer.
For the sake of simplicity,
we’ll continue to refer to it as a Transmitter.
A Pressure Transmitter requires a power supply to operate.
Most Pressure Transmitters are two-wire types.
Transmitters are also available as four-wire types.
As the name suggests, a two-wire pressure transmitter has only two wires.
These two wires provide power for the transmitter and are also the signal lines!
A four-wire transmitter has two wires connected to a power supply
and two signal wires connected to the PLC.
The power supply can be AC or DC depending on the vendor and model.
Alright, let’s wire a Gems PS41 series pressure switch
to Input 3 of a ControlLogix 1756-IB32 digital input module.
All of the Ground terminals on the 1756-IB32 module
must be wired together and connected to the negative DC terminal
of the twenty-four volt DC Power Supply.
So, we need to connect terminals 17,18,35 and 36,
and wire them to the -DC terminal of the power supply.
Because the pressure switch is not voltage-dependent,
it doesn’t matter which wire goes to the +DC [positive terminal of the power supply
and which wire goes to the terminal 4 of the input module.
So, take your pick and connect the two wires.
The 1756-IB32 module is capable of supporting up to 32 digital input devices.
Each additional device would be wired the same as the Gems pressure switch.
One terminal of the new device would connect to the +DC terminal of the power supply,
and the other device terminal would connect to any of the remaining open inputs
on the digital input module.
OK. Let’s move on to wiring Pressure Transmitters to a PLC Analog Input Module.
We’ll look at wiring a two-wire Wika E-11 Pressure Transmitter
to a ControlLogix 1756-IF8 analog input module.
On the Transmitter, the Red lead is Current in,
and the black lead is current out.
The analog module can be wired in two possible modes:
Single-ended or Differential.
The selection is important as it determines how the module is physically wired.
Our module is configured for Single-Ended mode.
In Single-Ended mode,
we can connect 8 two-wire transmitters sharing one power supply.
Each transmitter connection is referred to as a “Channel”.
The 1756-IF8 module
is configured for current input during programming in the I/O configuration.
We will connect the Wika E-11 two-wire transmitter
to Channel 5 of the analog module.
Terminals 9,10, and 13 of the analog module are connected
and then wired to the -DC terminal of the twenty-four volt DC Power Supply.
The Red lead of the Wika E-11 pressure transmitter
is wired to the +DC terminal of the Power supply.
The Black lead of the transmitter is wired to Terminal 14 on the analog module.
As we said earlier, more two-wire transmitters sharing the same power supply
can be connected to the analog module.
Let's add another pressure transmitter to the 1756-IF8 module.
We will connect another Wika E-11 two-wire transmitter to Channel 6.
Terminal 15 is wired to Terminal 13 of the analog module.
The Red lead of the pressure transmitter is
wired to the +DC terminal of the Power supply.
The Black lead of the transmitter is wired to Terminal 16 on the analog module.
Details on how to wire more transmitters
can be found on the Rockwell Automation website.
You can find the link to this PDF file in the video description.
Field wiring diagrams vary between companies.
In this example, two channels of the 1756-IF8 are wired in Single-Ended Mode.
Pressure Transmitter ZT-P3606 is connected to Channel 0,
and ZT-P3610 is connected to Channel 1.
Both transmitters share the same positive twenty-four volt DC Power Supply.
Let’s review:
in process control and instrumentation,
the terms Transmitter and Transducer are often used interchangeably
A transducer is a device that converts one form of energy
to an electrical or electronic signal.
A Pressure switch is a two-part device
consisting of a sensing transducer and an electrical switch.
A Pressure Transmitter is a two-part device consisting of a sensing transducer
and a circuit that transmits a standard instrumentation signal
which in most applications is 4 to 20 milliamps.
Most Pressure Transmitters are two-wire types
having two wires that provide power for the transmitter and are also the signal lines!
PLC analog input modules can be wired in two possible modes:
Single-ended or Differential.
The selection is important as it determines how the module is physically wired.
In Single-Ended mode,
two-wire transmitters can share a single power supply.
That should do it for this video!
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