Answer / guest

Resistanc Temperature Detector(RTD)encorporates two basic
concepts

1)Variation of temperature varies the resistance of Pt wire.
2)Variation in resistance affects the balancing of DC
bridge circuit.

For measurement purposes lead wires are brought out to make
external connections.These lead wires have some resistances
which affects the bridge balancing.

Since we can not reduces the resistances of lead wire to
zero.So, either 3 wire or 4 wire connection is employed to
ELIMINATES THE IMBALANCING TO THE BRIDGE CIRCUIT caused by
resistances of lead wires so that an accurate measurement
can be made.These wires(3 or 4) are called compensating
leads.

Author:arbelectbit@yahoo.com

Answer / sam

You are right, and the temperature indication does not
increase so significantly that it is worth the effort to use
a 3 or 4 wire RTD.
It might increase with something like 0,001Deg C so that is
so small you might as well say there is no difference in the
accuracy of a 2,3 and 4 wire RTD, using a local or smart
transmitter.
In the old days we use to use a 2 wire RTD in the field and
then run a cable say 200m to the temperature indicator. By
the time it gets to the indicator the temperature is
completely different from what it was in the field due to
the cable resistance that add itself the the RTD resistance.
We compensated for that by installing a 3de wire for the
sole propose to measure the resistance of the cable itself
and deduct that from the total resistance measured at the
temperature indicator.
So the actual resistance of the RTD as measured at the
temperature indicator is RTD - RLine1.(or [(Rline1/2)x2]if
you want)
With the 4 wire it makes it more accurate in that you can
now measure line one and line 2. The theory is that the one
line might have a small difference compare to the other line.
So the actual RTD resistance at the temperature indicator is
measured RTD - [(RLine1/2)+(RLine2/2)]
But since we all use the small compact local and smart
temperature transmitters these days, 3 and 4 wires are no
longer needed since the distance from the RTD to the
transmitter is only from about 50 to 500mm and but it seems
it have stayed due to some design engineer always saying,
why buy a 2 wire if you can get the 3 and 4 wire for just
about the same price. It will make the indication just more
accurate, but they never say by how much (0,001Deg C)
Good luck

Answer / maswood alam

Actuly there is little diffrence b/w 3 wire nd 4wire, 3wire
has 95% accurcy nd 4 wire has 100% but 4 wire more costly nd
both are use as long distance so we genarally prefared 3
wired RTD System......

What is the purpose of valve positioner. Explain 4 uses.

2 Answers   SRACO,

---

pl give the guidance for DUBAL written test

1 Answers  

---

What is the DIfferences between SMART transmitters and PROFIBUS DP/PA Transmitters?

4 Answers  

---

Explain the use of hair spring in the pressure gauge.

0 Answers  

---

What types of Instrumentation Related Questions can an Interviewer ask in a Telephonic Interview ?

0 Answers   Cairn, Honeywell,

---

DEAR SIR/MADAM MY NAME IS ARKAPROVA BHATTACHARYYA.I AM A FRESHER INSTRUMENTATION ENGINEER.CAN YOU PLEASE SEND SOME QUESTION PAPERS OF GRADUATE ENGINEER TRAINEE EXAM OF DVC(DAMODAR VALLY CORPORATION).MY EMAIL IDs ARE arka_aec@rediffmail.com.

0 Answers  

---

.==PL..PL.. FORWARD TO MANAGER PURCHASE./ / Q.ASSU. DEPT.. =FROM==AJAY ENTERPRISES ===============PUNECITY..INDIA. DEAR SIRS,............. ======================================================== =NEW SUPPLY/ REPAIRING AND CALIBRATION =OF=MECHANICAL /DIGITAL / ELECTRONIC=PRECISION MEASURING INSTRUMENTS=FROM == 22YEARS. ============================================================ = 1.==NAME OF THE COMPANY= AJAY ENTERPRISES 2.=ADDRESS OF THE COMPANY= OFFICE NO 08, DALAL CHAMBERS, MKTYARD PUNE= 411037. ===== TEL- 020 242601! 09. MOB- 0 98900 98941. 3.=EMAIL= ajaygujar1@gmail.com.-- AND-- ajayenterprises1@yahoo.com--- =========================================================== 4.=ACTIVITY OF THE COMPANY= SUPPLIER OF PRECISION MEASURING INST RUMENTS AND MAGNETIC TOOLS IN PUNE== [ MITUTOYO / TESA / KUMAUN / MAHR / BRITOOL / TOHNICHY / DIATEST-GERMANY / IMADA / TECKLOK / SYLVAC /ADITYA=ACCURATE / BAKER/ CRYSTAL / FLUKE-RAYTEK ETC. 5.=SUPPLY= VERNIER CALIPERS / MICROMETERS / HEIGHTGAUGES / SLIPGAGE / BORE DIAL GAUGES / MEASURING PINS / TORQUE WRENCHES / GAUGES.. PLUGGAUGES / RINGGAUGES / SHORE A / D HARDNESS TESTERS / DIAL THICKNESS GAUGE / FEELER GAUGES / ELECTRONIC COMPARATORS WITH PROBES / DFTMETERS / SURFACE ROUGHNESS TESTERS / DIGITAL= COATING THICKNESS METERS / PROFILE PROJECTORS /.. WE ARE ALSO DEAL IN == DIGITAL TACHOMETERS / =MULTIMETERS! / VIBRATION METERS / MEGERS- INSULATION METERS / =TE! MPRATURE INDICATORS / SOUND-LEVEL METERS / ETC... =AGENCY- FLUKE- RAYTEK.. MECO....LUTRON...KYORITSU....RION... ..................KELIEWS......AND MANY MORE ===AJAY GUJAR ...AJAY ENTERPRISES =08 DALAL CHAMBERS MKTYARD ROAD NEAR NISARG KARYALAYA =MARKETYARD PUNE= 411037.. =TEL= 020 2426 0109. =MOB=09890098941. =EMAIL=AJAY.MITUTOYO@GMAIL.COM =WEB--WWW.GUJARWORLD.COM

1 Answers  

---

WHY WE NOT USE 2-20mA,1-20mA,3-20mA or 10-50mA SIGNAL? INSTEAD OF 4-20mA.

6 Answers   Hindustan Unilever Limited, Yashmun Engineers,

---

Why hunting will occour in control valve?

6 Answers  

---

What are securities of turbine?

1 Answers  

---

what is remote mount with MTA option? (In case of Dual Sensor Vortex Flowmeter,rosemount has written in its catalog drawings).

2 Answers  

---

What is the input impedence of an OPAMP as an ideal device.

1 Answers   CCIE,

---