Instrumentation Question:

Answer #1
Generally in a transistor some amount of voltage is required for turning it on. This voltage is the cut in voltage. Up to this voltage the exists a nonlinearity in its characteristics. Beyond this cut in voltage the char. of transistor is linear. This nonlinear region lays between 0-4ma, beyond 4ma it linear. This is why 4-20 ma range is used.

Answer #2
Yes

Answer #3
If the control cable is get damaged then it will report to plc ( controller)...so it will help to know it is not communicating...

Answer #4
As voltage signal is affected by an external noise but current cannot be affected that's why 4-20 mA signal is preferred.

Answer #5
because when a signal wire 0-10v goes too far or too long there' s a voltage drop. but if you used 4-20mA current signal you will get the same signal of 4-20mA even your signal cable is very long.

Answer #6
yes

Answer #7
If a transmitter output is voltage the voltage is only accurate at the output of the transmitter. There will be many voltage drops throughout the loop so the input device will only see part of the voltage because it is only one of the voltage drops. Current is the same in all parts of the loop so the current a transmitter puts out will be the same at the input card. Voltage loops have not been used for many years because of this problem. Also, 4 ma is used so the Zero is Live allowing the loop to detect a problem if there is no voltage.

Answer #8
Addition to that, as a operating of channel, it is essential to confirm that it is working if we check it is 4 mA. Otherwise, 0 mA can me mislead to us for working of channel.