Answer / carl_ellis

An offset in readings from separate RTD's can indicate
- a difference in calibration of the analog input devices
- a bad RTD element, one that has drifted out of spec
- a common ground issue with ground loops between the analog
input devices

An RTD is supposed to be ungrounded and the two RTD's in a
duplex element are supposed to be electrically isolated from
one another, so it is unlikely the ground loop is unlikely
unless poor wiring of the extension wire or head wiring has
created a connection to ground.

If you're complaining about a small difference of the
indicated temperatures, then get out your cal gear and cal
the inputs.

To check for a bad RTD, I'd take an ohmmeter and see if any
leg on the A side has any connection to the B side by
disconnecting the wiring from each analog input and check
the resistance. If there's a low resistance, it indicates
some connection from A to B. If the extension wires are
then disconnected and the resistance is checked on the RTD
lead wires and the resistance remains, then it's a bad RTD.
If the resistance goes high (open circuit) then the
extension wire is shorting or making a low resistance
connection somewhere.

Carl Ellis
Measure First

how can calibrate vacume trasmitter by HART COMMUNICATOR ?

3 Answers   Bajaj, IMECO,

---

pressure switch range 0 to 2bar.i have to install from ground level to 5 meters height.what is the formula the to increse the range ? and every 1 meter how much pressure should be add ?

3 Answers  

---

How can you convert an SR Flip-flop to a JK Flip-flop?

1 Answers  

---

what is difference between HART communication and BRAIN communication?

1 Answers   Delta Controls,

---

What is pre-commissioning and commissioning ?

1 Answers   Armco,

---

why we use the 4-20 mamp signal used for transmitter.

5 Answers   Tecnimont,

---

PLEASE PROVIDE SAMPLES OF CHEVRON SKILL TESTS

0 Answers  

---

what is dead weight tester and where it is used?.

11 Answers   DuPont, Jain steels,

---

i am going to attend ongc exam this coming june for Graduate Engineer Trainee post if anybody knows the question pattern or have experience plz share it with me

3 Answers   ONGC,

---

hello can yoy pls send me previous papers of jindalpower and steel ltd.....'m from instrumentation..... mani1048@gmail.com

0 Answers  

---

What is the standard height for stancion supports? and what is the standard mounting height for different transmitters?

11 Answers   Samsung,

---

what difeerent between HART and BRAIN?

3 Answers  

---