Twisted Pair Thermocouples Principle

As you say, twisting is to eliminate noise. Maybe you will get some useful info from this paper...

http://www.acromag.com/sites/default/files/Basics_of_Temperature_Measurement_Using_Thermocouples_911A.pdf

Shreedhar.

My specific question was the following: how twisting the magnetically dissimilar wires such as Chromel (non magnetic) - Alumel (magnetic) achieves an E/mag field (we use it inside the electric machine) interference noise cancellation?

Can you advise? My view, that is does not.

Frankly, i have no firsthand experience in this, except to the extent of telling my lab technician to twist the ends. As per this part of the document whose link i gave...

Twisted shielded pair has very good immunity to noise pickup. Think of an untwisted pair as a loop of wire that behaves as a single turn transformer secondary winding. Twisting it causes cancellation of the magnetic pickup. The grounded outer shield keeps out electrical fields. The shield should be grounded at one end only to prevent ground currents.

Rixter.

My specific question was the following: how twisting the magnetically dissimilar wires such as Chromel (non magnetic) - Alumel (magnetic) achieves an E/mag field (we use it inside the electric machine) interference noise cancellation?

Can you advise? My view, that is does not.

Alex

Here both conductors are the part of the same loop and the current flow is same through both conductor. So it doesn't matter what the material is.

Magnetic field is directly proportional to the current flow. So will get cancelled each other.

Justin.

Good answer, but.. thermocouples are open-ended at cold junction. So, if both ends were connected, hot and cold the common current would flow through the circuit. However, the cold end is open, usually connected to the high impedance measurement device. So why bother twisting the wires?

Alex

Effective magnetic field around both the wires running side by side [of the same circuit] has nominally zero; normal 2 wire cable.

But if those twisted it bwill ecomes better cancelliom and used in Tests and Measurements.

Remember that Clamp-on Current meter only reads if clamped around a single wire.

If clamped around both the wires it will read zero.

For your intrest probes are made to measure current by inserting it between the wires.

It will read double the current?

Try to understand by drawing field around and inside of 2 wires.

Haajee. A thermocouple is open at cold end, connected to the High Impedance reading device. So there is no current flowing. If you know different, please explain.

Thank you

Alex

Yes it is open if not in use.

When connected in system it is loaded no matter how high the impedance is.

Simple example is in natural/ petrolium gas [As 'gas' may not be mixed with 'gas'

spoken for petrol in US] Flame sensing is through a thermocoule which drives and holds the Gas-Valve if the flame is there. as soon as flame extinguishes the Gas-Valve is shut.

Before starting the flame Gas-valve is kept open manually with a button, held for some time to work the thermostat.

There is difference between Thermocouple and a thermal switch.

Sorry.

There is no such Thermocouple System but there are cables for thermocouples of this description which has certain advantages in measurement. Not only in temperature but all electrical and electronic measurements.

like:

Temperature Sensors

Testing / Laboratories ie professional testing

New Plant Construction -Warrantee

General Industry (mills, refractories, etc) -Troubleshooting

Twisted shielded pair allows for a tighter bend radius, reduced crosstalk and reduction of EMI

And one advise:

Please do not put Answers @ Yahoo in CR4 discussions.

and try to search to learn and impart what you know or have in your stock.

Never hesitate to question hide what you know.

I am subscriber to yahoo answer and get such questions which may not be properly put.

Have fine time to learn and impart. Good luck!