Pressure transducers are widely used in various industrial applications for measuring the pressure of gases and liquids. The 4-20mA pressure transducer is the most commonly used one due to its reliability and ease of use. In this article, we will discuss the wiring diagram of a 4-20mA pressure transducer in detail.
What is a 4-20mA Pressure Transducer?
A 4-20mA pressure transducer is a type of pressure sensor that generates an electrical signal proportional to the pressure being measured. The electrical signal is then transmitted to an instrument, such as a PLC or a DCS system, which converts it into a pressure reading. The 4-20mA signal is widely used in industrial automation and control systems due to its high accuracy, reliability, and resistance to electrical noise.
How Does a 4-20mA Pressure Transducer Work?
A 4-20mA pressure transducer works by using a sensing element, such as a strain gauge or a piezoelectric crystal, to convert the pressure into a mechanical displacement. This mechanical displacement is then converted into an electrical signal by a signal conditioning circuit, which typically includes an amplifier and a current source or sink.
The current source or sink generates a current that is proportional to the pressure being measured, with 4mA representing the minimum pressure and 20mA representing the maximum pressure. This current is then transmitted through a two-wire cable to the receiving instrument, where it is converted into a pressure reading.
What are the Benefits of 4-20mA Pressure Transducers?
There are several benefits of using 4-20mA pressure transducers, including:
- High accuracy: 4-20mA pressure transducers offer high accuracy and resolution, making them ideal for applications that require precise pressure measurements.
- Reliability: 4-20mA pressure transducers are highly reliable due to their simple design and ability to withstand harsh industrial environments.
- Easy integration: 4-20mA pressure transducers are easy to integrate with other automation and control systems, making them ideal for use in complex industrial environments.
- Resistance to electrical noise: 4-20mA signals are less susceptible to electrical noise than other types of signals, making them ideal for use in noisy industrial environments.
Wiring Diagram of a 4-20mA Pressure Transducer
The wiring diagram of a 4-20mA pressure transducer is relatively simple, consisting of two wires that transmit the current signal and a third wire that provides power to the transducer. The wiring diagram typically includes the following components:
Power Supply
The power supply provides power to the pressure transducer and is typically a 24V DC power source. The power supply is connected to the transducer using a two-wire cable, with one wire carrying the positive (+) voltage and the other wire carrying the negative (-) voltage. The power supply should be capable of providing sufficient power to the transducer, typically around 10-30mA.
Current Loop
The current loop is the main component of the wiring diagram and consists of two wires that transmit the current signal. The current loop is typically a two-wire cable, with one wire carrying the current signal (4-20mA) and the other wire serving as the ground. The current loop should be connected to the transducer using a screw terminal or a DIN connector.
Receiving Instrument
The receiving instrument is the device that receives the 4-20mA signal from the pressure transducer and converts it into a pressure reading. The receiving instrument is typically a PLC, a DCS system, or a pressure gauge. The receiving instrument should be connected to the current loop using a two-wire cable, with one wire carrying the current signal (4-20mA) and the other wire serving as the ground.
Wiring Diagram of a 4-20mA Pressure Transducer with HART Protocol
HART (Highway Addressable Remote Transducer) is a digital communication protocol that allows for bi-directional communication between a field device, such as a pressure transducer, and a control system, such as a DCS or a PLC. HART protocol is often used in applications that require additional diagnostic and calibration capabilities. The wiring diagram of a 4-20mA pressure transducer with HART protocol is similar to the standard wiring diagram, with the addition of two wires for the HART communication:
HART Communication
The HART communication is typically a two-wire cable, with one wire carrying the HART communication signal and the other wire serving as the ground. The HART communication is used to configure and control the pressure transducer, as well as to transmit additional information, such as diagnostics and calibration data. The HART communication should be connected to the receiving instrument using a dedicated HART modem or a HART-enabled input/output (I/O) module.
Frequently Asked Questions (FAQ)
| Question | Answer |
|---|---|
| What is the difference between a 4-20mA pressure transducer and a 0-10V pressure transducer? | A 4-20mA pressure transducer generates a current signal that is proportional to the pressure being measured, while a 0-10V pressure transducer generates a voltage signal that is proportional to the pressure being measured. 4-20mA signals are less susceptible to electrical noise than 0-10V signals, making them ideal for use in noisy industrial environments. |
| How do I calibrate a 4-20mA pressure transducer? | To calibrate a 4-20mA pressure transducer, you will need a pressure calibrator, which is a device that generates a known pressure. You will also need a multimeter, which is a device that measures the current signal. Connect the pressure calibrator to the pressure transducer and adjust the pressure until the current signal matches the expected value (i.e. 4mA for minimum pressure and 20mA for maximum pressure). |
| Can I use a 4-20mA pressure transducer with a 120V AC power supply? | No, you should not use a 4-20mA pressure transducer with a 120V AC power supply, as this can damage the transducer. 4-20mA pressure transducers typically require a 24V DC power supply, which should be used instead. |
