Can I get RTD sensor with the wire length of 25m?

------Question for TT4-PT1000B-T125-M5-500 Please Put your question below------

Hi,
I need a RTD sensor preferable with this ring type probe and 25m cable length …
Is it possible to get this? If yes, what are the drawbacks for using 25m wire length?

Thanks.

Hello @gowtham_li,

Yes, it can be done. As an example, let’s consider this TM101-AACCB2GC2C1A1 Endress+Hauser as pictured below.

The datasheet suggests several ways to configure the sensor as show below including 3-wire and 4-wire configurations. Given your 25 M (82 feet) requirement, I would recommend the 4-wire configuration.

There primary reason for the 4-wire connection is to mitigate the resistance of the wire. Recall that an RTD typically has a low resistance with 100 Ω and 1000 Ω being the most common. With a long wire run, the wire resistance is an appreciable component of the overall resistance resulting in an undesirable measured temperature offset. With a 4-wire connection we separate the current carrying and the measurement wires. Here, one set of wires carries the excitation voltage - the current used to develop a voltage drop across the RTD element. The other pair of wires returns this voltage to the measurement system. It’s important to recognize that this return pair has nearly zero current. Consequently, we can obtain a true measurement.

Interference will also be an issue with the long wire run. If we assume random noise, you may be able to use digital filtering measurements. For example, we can average 16 or even 256 consecutive measurements to reduce the noise.

The 4-wire method may be used with smaller RTD including the lowest cost surface mount devices.

Did this answer your questions? If not, please let us know more about your application so that we may better assist.

Best Wishes,

APDahlen

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Hello @APDahlen , Thanks for the detailed explanation,

Please find the details of my application:
We want to monitor a temperature of a Light system using a Delta PLC, we chose a module -AS04RTD and the distance between the control panel and light system is max 15m, and this PLC module only supports 2wire or 3wire sensor. so, I was thinking we can use a ring type RTD sensor to screw it on the body of the light system to monitor.

So, is it okay to use a 3wire or 2wire sensor for this application,
Do let me know if you have any better ideas for this application,
Thanks for sharing.

Hello @gowtham_li,

Yes, it looks like you are limited to 2 or 3 wire:

You may be able to remove the cable resistance from within you PLC code. It’s not ideal and may be a moving target as the cable ages. However, it may be suitable for your application. Remember that there are two problem including cable resistance and noise. Calibrate out the resistance and use an averaging filter for the noise. Finally, be sure to watch out for ground loops.

As for other solutions, have you considered MODBUS? Many PLCs are equipped with this communications capability. You may be able to use a remote carrier such as pictured below with an RTD card. With this system, the sensor to converter wire run is short. The longer wire run is for RS-485 communication which is relatively incensitive to noise. Don’t forget a small 24 VDC power supply for the remote.

Sincerely,

Aaron

gowtham_li

Thank you for your patience while I was in contact with the product manager and supplier.
Here is the information I received:

For such a long sensor we would most probably need to use a double insulated round cable instead of two single insulated twisted wires.
Could you please check what is the quantity to quote?

Please have the customer review and advise.

Thanks Craig

Hello @gowtham_li,

There are many cables to choose from as seen in this list. A common solution is single pair with a foil shield plus third wire.

However, given your distance, you may want to consider a full shield such as this 20 AWG pair:

As for purchasing please use our main page, sales@digikey.com, or call 800-344-4539.

Please let us know if we can assist.

Sincerely,

Aaron

Hello Craig,

I need this sensor first - [1912-TT4-PT1000B-T125-M5-500-ND],
Qty: 20,

But before going with this purchase, I need single piece so that i can test it with our hardware and software,

Please share me the quote for both to this mail id - gowtham.rs@lucidimaging.in

Thanks,
Gowtham.

Hi Aaron,

I considered this method; we can’t keep the RTD card near the light system, as it is a printing machine it’s not standard to use there.
Thanks for the suggestion

Sincerely,
Gowtham

2 Likes

Hello Gowtham,

DigiKey is an e-commerce entity.

As a rule, small orders are entered via a web-based shopping cart or over the phone. Please know that there is a necessary divide between the technical division and the sales division as it allows each to group to focus and develop strength.

Please place your order via our main page main page at DigiKey - Electronic Components Distributor or call 800-344-4539.

Sincerely,

Aaron

1 Like