Answer / carl_ellis

My friend Dan has an article on why HART needs a minimum 
resistance in the loop to work.

http://blog.lesman.com/2011/10/06/add250-ohm-resistors-to-make-hart-work/#more-68

In summary, the loop power supply acts as a very low pass filter that tends to filter out the HART signal. 

According to the HART Foundation spec, the 1200-2400 Hz HART signal needs a minimum (230 ohm) resistance in the loop to create a HART signal with enough amplitude to meet the sensitivity requirements of a HART modem receiver. 

Carl Ellis
Measure First

Answer / nilesh bhatt

Hart communicator work wen it gets minimum 5 volt and when it connects with 250 ohm resistance it gets excited and works online or offline.

Answer / saurabh singh

1-5 volt standard voltage for hart operation.
4-20 ma standard current signal
When 4ma* 250v= 1 volt
20ma* 250v = 5 volt
At 5 volt hart comes in operation.

Answer / nitesh kumar

Because  250 ohm resistance converted 4-20 mA  standard current signal when we connect 250 ohm resistanc in parallel of 1- 5 volt supply..

While preparing the graphic diagrams trend display, 3 types of trends are prepared by Yokogawa system vender. These are for process variable, manipulated variable & set point variable. Why these 3 trends are required? Explain the purpose of these 3 trends.

1 Answers  

---

define SIMULATION a and what is the need of it

3 Answers   Siemens,

---

any body who gone thru recent iocl interview.INSTRUMENTATION questions. I need.

0 Answers   IOCL,

---

1 > HOW TO MEASURE INTERFACE LEVEL 2 > DIFFERENCE BETWEEN RADAR & ULTRASONIC LEVEL TRANSMITTER

3 Answers   Atul Auto,

---

pressure gauge measure static pressure or dynamic pressure?

3 Answers  

---

How an rtd work, and what volts/current goes to a rtd to measure the resistance?

0 Answers  

---

what is loop folder?

1 Answers   Bapco Bahrain Petroleum Company, Hyundai,

---

what is sinking and sourcing....

2 Answers  

---

field bus transmitter calibration procedure tell me

0 Answers   BAP,

---

If a normal magnetic type flow transmitter that can measure flow, temperature and show this parameters on field, is it possible by any means to get this (flow and temperature) parameters info. On dcs? And if yes then with HART, FO communication or any other communication system?

1 Answers   Process Control Technologies,

---

Why is it necessary to use compensation leg to measure the liquid level in a closed or pressurized tank?

0 Answers  

---

what is loop?

4 Answers  

---