There are many types of sensors which transmits information in industrial process applications. A sensor is a device used to measure physical parameters such as level, pressure, temperature, liquid flow rates etc. Transmitting sensor information via a current loop is very useful when the information has to send to a remote location over long distances.
As we see in this figure, A typical 4-20mA current loop circuit is made up of four elements.
(1)Sensor
(2)Transmitter
(3)Power supply
(4)Controller
Sensor provides an output voltage whose value represents the physical parameter being measured(for example, temperature measured by thermocouple). The transmitter converts the voltage into an current signal. The process monitor or controller further converts this current signal(4-20mA) into a voltage signal which can be further processed. The loop power supply generally provides operating power to the transmitter, receiver and to other loop components. +24V is the most widely used power supply in 4-20mA process monitoring applications.
Why 4-20mA Why Not 0-20mA?
Let us consider a thermocouple is measuring a temperature of (0-100°C), By using 0-20mA standard when the temperature is at 0° the transmitter produces the signal of 0mA and at 100°=20mA. In the case of wire break, sensor failure also it produces the same 0mA & in the case of 0°C also it produces the same signal. But if we see at 4-20mA standard, When the temperature is at 0°C it produces the 4mA signal and when there is a wire break or any failure in the sensor it produces 0mA signal.
In 0-20mA standard, We cannot differentiate between the minimum and break down. Another drawback is,If we are using 0-20mA signal we have to supply power to our loop components using one or two more power supply lines. But with 4-20mA signal we always have atleast 4mA flowing in the loop. With this we can power our loop components and we can have our power supply and signal on the same pair of conductors. These are the some major reasons for using 4-20mA signal.
Why Current Signal Over Voltage Signal?
The signals are transmitted from the field to the control room and viceversa. The value of cable resistance is directly proportional to the distance of transmission. If 0-10V is transmitted over long distance, Due to the resistance of cable there will be drop in the voltage and the signal received at the controller will not be accurate and Noise interference will be High in voltage signal. Whereas, Current signal can be transmitted over long distances without any loss of accuracy and Noise interference will be Less in current signal. To overcome this drawbacks, 4-20mA is preferred over 0-10V, 0-5V.
ADVANTAGES OF CURRENT SIGNAL:
1)Lower cost.
2)Less wiring.
3)Better noise immunity.
4)Can travel over large distances.
5)High accuracy.
Thanx for reading..
As we see in this figure, A typical 4-20mA current loop circuit is made up of four elements.
(1)Sensor
(2)Transmitter
(3)Power supply
(4)Controller
Sensor provides an output voltage whose value represents the physical parameter being measured(for example, temperature measured by thermocouple). The transmitter converts the voltage into an current signal. The process monitor or controller further converts this current signal(4-20mA) into a voltage signal which can be further processed. The loop power supply generally provides operating power to the transmitter, receiver and to other loop components. +24V is the most widely used power supply in 4-20mA process monitoring applications.
Why 4-20mA Why Not 0-20mA?
Let us consider a thermocouple is measuring a temperature of (0-100°C), By using 0-20mA standard when the temperature is at 0° the transmitter produces the signal of 0mA and at 100°=20mA. In the case of wire break, sensor failure also it produces the same 0mA & in the case of 0°C also it produces the same signal. But if we see at 4-20mA standard, When the temperature is at 0°C it produces the 4mA signal and when there is a wire break or any failure in the sensor it produces 0mA signal.
In 0-20mA standard, We cannot differentiate between the minimum and break down. Another drawback is,If we are using 0-20mA signal we have to supply power to our loop components using one or two more power supply lines. But with 4-20mA signal we always have atleast 4mA flowing in the loop. With this we can power our loop components and we can have our power supply and signal on the same pair of conductors. These are the some major reasons for using 4-20mA signal.
Why Current Signal Over Voltage Signal?
The signals are transmitted from the field to the control room and viceversa. The value of cable resistance is directly proportional to the distance of transmission. If 0-10V is transmitted over long distance, Due to the resistance of cable there will be drop in the voltage and the signal received at the controller will not be accurate and Noise interference will be High in voltage signal. Whereas, Current signal can be transmitted over long distances without any loss of accuracy and Noise interference will be Less in current signal. To overcome this drawbacks, 4-20mA is preferred over 0-10V, 0-5V.
ADVANTAGES OF CURRENT SIGNAL:
1)Lower cost.
2)Less wiring.
3)Better noise immunity.
4)Can travel over large distances.
5)High accuracy.
Thanx for reading..
Have a good day :)
Submersible Level Sensor made with PVC | PP | PVDF | PTFE | 316L SS material and an electrical transmission indicate the liquid level. Bullet, cage, and flush tip models are available. Working with water tank, sumps, reservoirs, down hole, oil tanks and lime slurry. There is a miniature submersible transmitter that is low power voltage.
ReplyDeletethanx for the information
ReplyDeleteHow long we can carry 0-10V signal...?
ReplyDelete