Q: Why most of analog o/p devices having o/p range 4 to 20 mA and not 0 to 20 mA? ( sai saikumar jn )

Q:Why most of analog o/p devices having o/p range 4 to 20 mA and not 0 to 20 mA? Ans: 4-20 mA is a standard range used to indicate measured values for any process. The reason that 4ma is chosen instead of 0 mA is for fail safe operation . For example- a pressure instrument gives output 4mA to indicate 0 psi, up to 20 mA to indicate 100 psi, or full scale. Due to any problem in instrument (i.e) broken wire, its output reduces to 0 mA. So if range is 0-20 mA then we can differentiate whether it is due to broken wire or due to 0 psi. Follow us at => www.facebook.com/saikumar544