Answer / carl_ellis

192 views of this thread up to this point, yet no one's
answered by Jan 2014.

I have read a reference to motor speed and direction
controller that use or used a bipolar +/- 20mA as an input
demand signal, but that's the only use I've ever heard of.

Bipolar +/- current signals are rare in the process
industries. Even the TTY teletypewriters of yesteryear
used a unipolar current loop, not a bipolar current.

That's not to say that it can't be done, and many industrial
analog inputs have bipolar +/- DC voltage functionality,
like -50 to +50mV, -1.0V to +1.0V, or -12 to +12V dc, and
Phoenix Contact has an instrumentation signal isolator that
has bipolar current output at +/- 20mA, but I haven't a clue
what one would use the bipolar function for.

Of course, pumping a bipolar current through a precision
dropping resistor would provide a bipolar +/- dc voltage
signal.

Carl Ellis
Measure First

WHICH IS BEST INSTRUMENTATION OR ELECTRICAL ENGG?

3 Answers   SAS,

---

what is the approximate cost of U tube manometer having range 1000mmwc to 1000mmwc?

1 Answers  

---

can any one pl explain me in brief that how we select the leakage classification in valve,means for liquid or gas there is any standard for selecting leakage classification or its depend upon valve size or any any other parameter.

3 Answers  

---

canu tell me why 4-20 ma and why not this 3-25ma?please give reason of this value.

6 Answers  

---

Difference between guide wave radar & non guide wave radar ?

1 Answers   UPL,

---

---

generally for transmitter we are giving supply 24vlts?but we are getting output 4-20ma ? how it is possible? is there any operation inside the tx?pls give complete information?

3 Answers  

---

How does one detrmine the direction of movement of core in an LVDT?

2 Answers   Honeywell,

---

what is virtual instrumentation

0 Answers  

---

What is the use instrument barriers? Can you give me review materials about this?

1 Answers  

---

Define cryogenic?

0 Answers  

---

How to Calibrate Coriolis Flow transmitter in field

0 Answers  

---

What are the advantages and benefits of using PLCs to automate a section of a plant?

2 Answers  

---