in any transimitter (flow/level) there are three terminals
for supply& test (+,-,+)in two wire,24VDC given to Tx.,but
how 4-20 ma signal travels thru same wire (as it is for
24VDC input supply)?
Answer Posted / karthik
24VDC is the driving voltage for the entire loop of the
transmitter. The loop consists of the supply, t/x and may be
some load resistance. The transmitter's min. working voltage
is around 12V. So t/x is bound to give a 4-20mA o/p based on
the range of the measured process variable if it has a
supply more than this min. value.
Primarily 24VDC is to drive the electronics associated with
the Primary sensing element present in the t/x.
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