Answer / carl_ellis

The 'test' connections on a 2 wire, loop powered pressure transmitter have a diode behind them.

If a milliampmeter is connected across the test terminals (in parallel with the diode), the impedance of the meter is less than the diode's, so current will flow through the milliampmeter. There is not enough voltage drop to forward bias the diode and the diode will not conduct with a low impedance meter circuit connected across it. The diode turns off and the current flows through the meter.

Test terminals are provided for loop troubleshooting so that loop current can be measured without breaking or opening the loop circuit so that the milliampmeter can be put in series in the loop circuit.

Carl Ellis
Measure First

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

2 Answers  

---

HOW TO CHOOSE FREAQUENCY IN FMCW TYPE RADAR INSTRUMENTS. DESIGN BASIS OR DESIGN CALCULATONS ?

0 Answers   Chevron,

---

What is upsampling and downsampling?

1 Answers  

---

testing of thermo-couple?

3 Answers  

---

what is skin thermocouple?

3 Answers  

---

---

Can we used Condensate Pot on flow transmitter which is using on liquid having sluge and DP transmitter is in pit and below the process line,Can we used Condensate pot for accamulate the Sluge?

1 Answers  

---

what is the tempareture conpensation?what is the use of this?

1 Answers  

---

What is the PLC Level & type.

2 Answers   Bhushan Power Steel,

---

difference between span and range

3 Answers   IOCL,

---

Why we used cage in control valve?

8 Answers  

---

Pl send the model question paper of mahagenco account officer post

0 Answers   MahaGenco,

---

Whatis the reset ofset and control system in instrumentation

0 Answers   Asyad International Company, CAE, Sugar Factory,

---