Answer / sivakumar d

Its Ohms's Law:

We need output: 4 to 20mA. corresponding voltage level is 1-5V

when Min Transmitter O/P

I=V/R =1/250 =0.004 =4mA

When Max Tranmitter O/P
I=V/R =5/250=0.02 =20mA.

So to get Standard Current Signal We need 250 ohms resistor.

Answer / anees

Because that Hart Calibrate need proper loop resistance
there for when we use in lab/Bentch calibration we need
it,otherwise in field calibration we doesnot needed

Answer / vinodkumar

when calibrating an hart transmitter in lab, we need a loop resistance between 250 ohms & 600 ohms, because without a resistor the HART communicator did not communicate with the transmitter. Because transmitter is a high impedance circuit with respect to the HART communicator. When HART communicator try to communicate with transmitter by producing a digital signal, the signal gets grounded through power supply and thus the signal didn't enter the transmitter without the resistor. When resistor is added, the transmitter become a low impedance circuit with respect to the resistor, so the signal produced by the HART communicator SHOULD have pass through the transmitter and so does the communication between HART communicator and HART Transmitter. Without the resistance between 250 ohms and 600 ohms the HART communicator did not communicate with Transmitter.
But in analog transmitters exact 250 ohms is used to convert 4 - 20mA to 1 - 5V respectively. For this only and exact 250 ohms is needed

Answer / md. afroz alam

To increase the loop of Resistance we use 250 ohms Resistance with smart transmitter in bench or lab calibration

Answer / g.ramesh

because of the load impedence it should need the 250
resistor at time only we are able to get the frequency
of 1200hz to 2200 hz

Answer / imran

According to Ohm Law V=IR .we need resistance for voltage
drop across Hart as current is there to energize Hart
circuit.and due to hart hat low impedence w.r.t XTMR .DCS
Cards hav builtin resistance that s why no need for
resistance in field

Answer / sandip

we r using 250 ohm resister to convert 4-20 ma output.

What is the difference between a PLC (Programmable logic controller) and DCS (distributed control system)?

7 Answers  

how in the 2 - wire transmitter, 24v supply and the 4ma signal gets in the same path?

1 Answers   Yokogawa,

How to consider the flow directions for control valve (Globe) Is the there any easy understanding in order to select the flow directions?

3 Answers  

what is the equation for gas flowmetering? whic includes gas flow, pressure, and temperature.

2 Answers  

what is scale factor of proximitor & unit of the vibration.

0 Answers   ADMA OPCO,

What is difference between Ionization heat and bimetallic heat

0 Answers   KOC,

what is hart communicater? can u give brief explanation about this issue?

3 Answers  

Sir i am preparing for PSU exam for ONGC but i am not able to get the appropriate syllabus and previous year question papers. Kindly send me the same, that will be a great help from ur side. OR if anyone can plz send me the papers and syllabus please.

11 Answers   Bhel, GAIL, IOCL, ISRO, NTPC, ONGC,

why we use -ve voltages in vibration prob?

1 Answers  

how does we calibrate a square root flow transmitter ,give an example and explain it step by step like range calculation , calibration hook up series connection , zero check , and how to apply pressure , and if not geting proportional output then what should we do ?

0 Answers  

what is the difference between plant earth and instrument earth? and what type of cable( cable size ) used for both? and why ?

0 Answers  

Can Any body tell me about the Contact or Email id of any good Consultancy which help me to find a job in Instrumentation Field in India .I have Six years of Work Experience in the Same field.Please revert me back on shammi_gwalior@yahoo.com ?

0 Answers