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

why is the sleeve of the cable used for?

2 Answers   Jindal,

---

which are types of orifice tap ?

2 Answers  

---

what will the sending unit in the fuel gauge utilizes?

0 Answers  

---

which flow meter is use for measuring the open channel flow?

2 Answers  

---

Any one can help me to identified, how can we interchange the device in FF

0 Answers   Ion Exchange,

---

what is pico fuse? how this different rom othe fuses and how to locate it inside the card?

1 Answers  

---

how works encoder in plc

0 Answers  

---

what are the steps I have to deal with?

0 Answers   ONGC,

---

waht is difference between pressure transmitter and transuducer

4 Answers   Gasco,

---

cascade controller is feed back or feed forward or both

4 Answers  

---

how can we caliberate interface level troll

2 Answers   Grasim, IOCL, KOC, Sankyu,

---

how can calibrate pressure transmeeter in the feild ?

1 Answers  

---