if the t/c o/p is 4-20mv then how plc recognize it
because we are dealing with the 4-20ma in the
plc ????????????????
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Answer Posted / arindam
why we require a 4-20 mamp for transmission? the main reason
behind it because of electro magnetic interference the
voltage can get interfered very easily and we can't get our
desired o/p value.when we are using 4-20 mamp this problem
is solved but since, PLC is a digital device it can
understand mainly High=5V or low so we design the sink to
have a resistance as high to get the desired voltage, the 4
mamp is also helpful to power the electronics at the
transmitter end. to have a 4-20 mv instead can firstly :
cause em interference and secondly we need to have a
continuous level monitoring for different voltages...which
can increase the size of PLC . Also because of change of
impedance at the transmission line the voltage can drop
below 4 volt ocassionaly then loop powering of field
instrument will not be possible.
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