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hi there,
just a quick question - can i use a 4 wire prt instead of a 3 wire one to do the same job? i have a 4 wire prt already and i was trying to interface it with a wheatstone bridge. however i now realise that i need a 3 wire for this. can i use 3 wires off my 4 wire prt and cut one wire off, or will i need to buy a new one?? any feedback much appreciated!!

regards,
jfox

You're on track. Cut off the extra wire.

A 4 wire RTD is a 3wire RTD with an extra wire.

Three wire & Four wire sensors provide compensation for lead resistance and It depend for the:
1-Accurcay of measurement & Applications.
2-The wiring 3 wire insted of 4 wire.
3-The hard ware " Multiplexer, Transmitter you must change the configuration.

When using a 4-wire RTD, the effect of lead resistance is eliminated and has no impact on accuracy. However, you can use 3 wires of a 4 wire RTD with reduced compensation for lead resistance. A 3-wire sensor will not fully cancel lead resistance error because it cannot compensate for imbalances in resistance between the lead wires.

Bryce

Hi
What is the function for 3rd wire? It means we can use 2 wire RTD at all. As I said 4 wire provides greater accuracy than the 3wire connection

you can use 4 wire RTD for 3 wire RTD systems also by connecting resistive element in 1 & 2 terminals and zero ohms wires 3 terminal. By using 4 wire RTD for 3 wire configuration you are loosing the lead wire effect or error compensation in the 3 wire configuration.

But it will serve your purpose.
with regards
E.M.V.Prasad

Jfox,

I think that a good practice is join together two wires from one extreme and don't cut the wire, because these wires are normally feeble and very thin. Then it can get broken very easy. Therefore it is like a future spare wire (the 4 wire). I mean the RTD wires are very fragile and can be broken even/including during the connection in the Xmtr or wheatstone bridge. This 4 RTD can work like a 3 RTD but I repeat consider not cutting the wire, keep it, join it together to the same terminal or let loose with insulating tape.

Regards,
J.Pinzon
Instrument Technician

Hi,

I have a basic question about connecting a 4 wire RTD to a data logging card. I have a 16 channel HP bench link data logger and a 4 wire (black and red wire) RTD. How do I terminate these 4 wires onto the data logger card???

Thanks,
shiraz

If I recollect properly, HP's BenchLink was a PC software package, not a piece of hardware.

What is the hardware device that you need to connect to? Do you have a link for the manual for the device?

Issac

The hardware is HP34970A

thanks.

It looks like it depends on which mux module you have.

From here you can download the 34970A User's Guide in pdf:
http://www.home.agilent.com/agilent/techSupport.jspx?pid=100000131 3%3Aepsg%3Apro&pageMode=MN&cc=US&lc=eng

It's really a pleasure to read decent documentation like Agilent's. All sorts of informative data like:

34901A 20-Channel Armature Multiplexer
• 20 channels of 300 V switching
• Connects to the internal multimeter
• For detailed information and a module diagram, see page 164.

Each of the 20 channels switches both HI and LO inputs, thus providing fully isolated inputs to the internal multimeter. The module is divided
into two banks of 10 two-wire channels each.

When making four-wire resistance measurements, channels from Bank A are automatically
paired with channels from Bank B . . . all channels on the module are break-before-make.

34902A 16-Channel Reed Multiplexer module
• Switching speed of up to 250 channels per second
• Connects to the internal multimeter
• For detailed information and a module diagram, see page 166.

Use this module for high-speed scanning and high-throughput automated test applications. Each of the 16 channels switches both HI and LO inputs, thus providing fully isolated inputs to the internal multimeter. The module is divided into two banks of eight two-wire channels each.

When making four-wire resistance measurements,
channels from Bank A are automatically paired with channels from Bank B. You can close multiple channels on this module only if you have
not configured any channels to be part of the scan list. Otherwise, all channels on the module are break-before-make.

page 23 pdf:
wiring connection diagram for 4 wire RTD, for either 34901A or 34902A input module

page 210 pdf:
For 4-wire RTD measurements (FRTD), the instrument automatically pairs channel n with channel n+10 (34901A) or n+8 (34902A) to provide
the source and sense connections.

For example, make the source connections to the HI and LO terminals on channel 2 and the sense
connections to the HI and LO terminals on channel 12. Specify the paired channel in the lower bank (source) as the scan_list channel.

Have fun.

Issac

Your question is very evident because when you have a 4 wire RTD you can apply that for any 2 or 3 wire measuring system.