What is the difference between a Wheatstone Bridge & Callender-Griffith Bridge in an RTD?

Question

What is the difference between them when used in a Resistance Temperature Detector (RTD) circuit. Wheatstone Bridge has a rheostat to balance the resistance, does the Callender-Griffith Bridge have a rheostat as well. Also why are three connecting wires used in the Callender-Griffith Bridge circuit. I've tried to find this elsewhere but they have just confused me more. All help is appreciated. I've asked the same in the Engineering Section too but that section is less popular so I thought I would try here. Thanks.

Callender-Griffith Bridge is also called Siemen's three-lead circuit if it is of any help.

Thanks for your help Sir. I am looking for information on Callender-Griffith Bridge. I am familiar with Wheatstone bridge. I have a circuit diagram of Callender-Griffith Bridge but it explains nothing significant as to why it is different from the Callender-Griffith Bridge. I appreciate the info on three wires. In the circuit diagram it shows the wires connected directly to the other two wires. I am not sure if it is in series or parallel. I would be grateful if you clarify this too. Thanks.

My bad. I have a circuit diagram of Callender-Griffith Bridge but it explains nothing significant as to how it is different from the Wheatstone Bridge

Answer 1

All metals will change in resistance when subjected to a temperature change. This relationship can be predicted by use of a constant (alpha) - the temperature coefficient of resistance. No two different metals have the same alpha and if the properties of the metal are known, a resistance vs. temperature curve may be established which can be accurately duplicated.

A metal's alpha may be changed by alloying it with another material or by mechanically stressing it. Thus, only a few materials are used for resistance temperature detectors (RTD). Other factors which limit the use of some metals and alloys as RTDs include: low electrical resistance, difficulty in forming coils, availability in the pure state, linearity of resistance vs. temperature curve, long-term drift and stability characteristics, resistance to contamination and chemical attack, etc. When all of these factors are considered, the most commonly used materials for RTDs are platinum and nickel. On special applications, tungsten and copper are also used.
The sensing element of a RTD may consist of a coil, foil or thin film deposited material. This sensing element may be wound or deposited onto a suitable insulating core and then encapsulated with an insulating material.

RTD extension leads may be of any convenient material (typically copper wire with insulation requirements to suit the environment of use) provided all leads are of the same material. The number of extension wires can consist of two, three or four wires. Two extension leads are used where the lead wire resistance is not very important. Higher accuracy is achieved if three wires are used - the third wire compensating for the lead wire resistance. Four leads are typically used only with dual element RTDs.
An RTD system consists of the sensor, lead wire and an instrument/readout device. This system is balanced at some convenient reference temperature (usually 68° F) before the sensor is exposed to the temperature of the test item. When the sensor is heated (or cooled), the bridge circuit is unbalanced by an amount directly proportional to the temperature of the test item.

Please explore the sites below.
Other uncommon bridge circuits are typically patterned from the Wheatstone Bridge.

I hope the new site that I had surfed will give you more info on your question. Please refer to section 6.2 on it.

http://en.wikipedia.org/wiki/Resistance_thermometer

In the Philipppines, particularly in USC where I'm connected, had no experiment utilizing Callender-Griffith Bridge.
But as I understand, it basically consist of the Wheatstone bridge. It matters only on the number and characteristic features of the lead wires used that are connected to the testing element, refer to the figure in section 6.2 on the recently surfed site.

Wheatstone stone bridge is also utilized in strain gauges where I am very much familiar especially I had a hands-on experience in constructing sensors using SR4-Strain Gauge when I was in Amsterdam last 1996.

Answer 2

Wheatstone Bridge Wiki

Answer 3

i don't know what answer your looking 4 wayne bridge is a rubbish left back torres is a striker out of form is this good enough 2 b the best answer???