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because 4 ma for live zero and at 20 ma no spark will generate and it is safe current this is why we use 4-20 ma and another thing is tx and cotrollers even plc and Dcs desinged to accept 4- 20 ma singal which is standard

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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


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.


4-20 ma loop testing?

Yes a 4 - 20 ma loop can be tested.


Why 4-20 ma is used in Analog Signals?

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.


Definition of 4-20 mA?

Previously when transmitters were configured for 0-20mA signal it was very difficult to identify an open circuit at 0mA,hence to supersede this defect it was decided to configure the transmitter as 4-20mA signal,so that if there is open signal it can be easily identified.


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.


Why 4-20 mA why not 3-19 mA for current output?

Because 4-20ma is an industry standard.


Standred voltage used for transmission of 4-20 ma signals?

4ma = 1v rising to 5v @ 20ma


When is Ipswish MA spring break?

Generally the week of 4/20.


What are the release dates for AnthonyMaTube - 2012 MA-tthias 3-20?

AnthonyMaTube - 2012 MA-tthias 3-20 was released on: USA: 4 August 2013


How do you calibrate smart transmitter for flow measurement?

use the communicator and apply 4 MA which is your zero them apply 20 MA which is your span. .


Can 4 - 20 mA be used to switch on and off 400 volt 3phase motor?

Yes but it has to be processed first. Programmable controller has the ability to take a 4-20 signal as an input and after processing close an output which can close a motor contactor.