0
Earlier, instead of 4-20 mA, 0-100 mA was used. But the usage of 0-100 mA led to sufficient power dissipation. Hence the upper range was reduced to 20 mA to optimize the power dissipation (this was found by experiments). In this way the upper limit was set. But this 20 mA is limited to cable length of 50 meters.
For the lower limit i.e. 4mA . Zero was not used as the lower limit because it give no intimation about actual zero value or zero transmission due to some breaks in the circuitry. Therefore 4mA was set as the lower limit as it is also above the maximum leakage current in electronic circuits. In some transmitters, some times the transmitter shows 2 mA. This is used to indicate that there is some fault in the sensor. Actual zero is indicated by 4 mA.
The scale is linear. For example, in a pressure transmitter of range 400bar.
0 bar - 4 mA
100 bar - 8 mA
200 bar - 12 mA
300 bar - 16 mA
400 bar - 20 mA.
The reason for not using voltage is that voltage continuously drops over the length of the wire whereas current can be transmitted over a given length without any drop.
The main purpose of using electrical quantities is transmission to remote locations.
What else can I help you with?
How many amps are in 420 mA?
There are .42 amps in 420 mA. Equation 420/1000 = .42 amps
Why is 4-20 mA used more often in analog signaling and not 0-20 mA?
The 4-20 ma is used more often in analog signaling than 0-20 ma because sufficient power dissipation. The hence is the upper rage and was reduced to 20 ma.
What type of transmitters are used in power plant DCS systems?
THE MAIN TRANSMITTERS USED FOR POWERPLANTS ARE FLOW,LEVEL,PRESSURE,TEMPRETURE,VIBRATION.THEY ARE LOCATED IN THE FIELD AND GENERATE 4-20 ma ANALOG SIGNALS.AFTER THAT THE SIGNALS ARE CONDITIONED,AMPLIFIED AS PER SYSTEM COMPATIBLITY,FOR FINAL CONTROLL
What devices uses anolog signals?
Generally process control devices use analog signal. Normally in an industrial automation setup, 0-20 mA (mili amp) or 4-20 mA or 0- 10 Volts are used. These signals are used for both providing control output and to provide feed back signal (say to a PLC (programmable logic controller) or DCS) Example for a control out put is a motorized damper operated by 4 - 20 mA signal. PLC provides 4-20 ma signal. Example of a feed back signal is 4 - 20 mA signal from temperature transmitter, measuring a liquid temperature to PLC as input.
What is a 4-20 ma is it a dry contact?
A 4-20 mA signal is an analog current loop commonly used in industrial automation to transmit sensor measurements over long distances. It represents the range of the measurement, where 4 mA typically indicates the lowest value and 20 mA the highest. This type of signal is not a dry contact; instead, it requires a powered loop and can provide continuous data transmission. Dry contacts refer to a switch that does not directly supply power, often used for simple on/off signals.
Standred voltage used for transmission of 4-20 ma signals?
4ma = 1v rising to 5v @ 20ma
Why 4 to 20 ma signals?
4 to 20 mA signals are commonly used in industrial applications for process control and instrumentation because they offer several advantages. This current range provides a clear distinction between zero and the lowest measurable signal (4 mA indicates the minimum value, while 0 mA is reserved for fault conditions). Additionally, current signals are less susceptible to noise and voltage drops over long distances compared to voltage signals, ensuring reliable data transmission. This standard also allows for easy integration of multiple sensors and devices in a control loop.
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Why do we use 4 to 20MA?
The 4 to 20 mA current loop is used in industrial process control because it provides a reliable way to transmit analog signals over long distances while minimizing the effects of electrical noise. The range starts at 4 mA to avoid confusion with a zero signal (0 mA), ensuring that any reading below 4 mA indicates a fault or disconnection. This standard also allows for easy integration of multiple sensors and devices into a single loop. Additionally, the use of current rather than voltage helps maintain signal integrity, as current remains constant regardless of the resistance in the loop.
Why use a 500 ohm power resistor?
500 ohm resistance is widely used to convert 4-20 ma current signals generated by a wide range of sensors into voltage signals. It provides 2 to 10 volts to the device. E=IxR.
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Southampton is a small town in Massachusetts, USA. Latitude, North: 420 13' 45" Longitude, West: 720 43' 50"
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Yes. Ma is a Scrabble word.
