أنشئ حسابًا أو سجّل الدخول للانضمام إلى مجتمعك المهني.
The 4-20 mA signal is used instead of 0-20 mA oR 0-16 mA for reasons as below:
1. For a 2 wire transmitter the device itselg requires some power for operation which is equal to 3.98 mA.
2. The 4-20 mA current signal helps to differentiate between live zero (Process parameter at 0) when Transmitter reading is 4 mA & Dead Zero ( Transmitter Fault Or Circuit faul) when transmitter readiing is less than 4 mA
because you cannot determine if the line is cut if you start with zero. And 4ma is what we called a livezero, because at that ampere rating is where the current is stable.
instrument transmission 4-20 ma is correct...
starting 4ma is transimission without dead
starting 0ma is transimission dead condication so using 4-20 ma.
beacuse in case of cable cut thier is no signal will be sent to teh control system - as in case of open signal if we use 0-20 ma or 0-16 ma- so it will make wrong indication
A good answer is already added by shipla joshi.
because of the live zero, where the standard voltage for electronics is 1v, 5v
4ma*250ohm=1v
20ma*250ohm=5v
the standard measurement of instrument 4-20mA which is 4mA equal to 0% and 20mA equal to 100% is used of 3 wire sinal cable 2 wire connected terminal to +/- 24vdc and 1 wire connected to 4-20mA terminal which fadeback to the HMI
because in case of 4-20 mA Zero output indicating an open loop condition(error condition). but for 0-20 mA we cannot identify actual zero output from open loop (line cute) condition. also 20 mA is used as maximum value( URV ) because the human heart can withstand up-to 30 mA of current only. so,as a safety point of view 20 mA is chosen
To ensure loop monitoring in case of cable failure. Also there NAMUR range to monitor connected device.
هل تحتاج لمساعدة في كتابة سيرة ذاتية تحتوي على الكلمات الدلالية التي يبحث عنها أصحاب العمل؟