RTD Transmitter
RTD Transmitter
(OP)
Is there ever really a good reason to use a 3 or 4 wire RTD card instead of a 4-20 mA temp transmitter? From what I read, the transmitter isn't expensive ($80-120 U.S), provides a signal that is more immune to noise, can be recalibrated easily for another RTD sensor (as opposed to matching the card to the RTD), and no special cabling is required. Were RTD cards used just because transmitters at the time were too expensive?





RE: RTD Transmitter
They introduce more span and zero errors. This can add to calibration hassles.
They can increase system space requirements.
They're yet another "thing".
They reduce reliability.
They cost more money.
Otherwise if none of these bother you they might be preferred.
A lot of systems I build for need 20 or 30 RTDs.. Wanna buy 20 or 30 transmitters? Not I.
I probably wouldn't use them unless I only needed a few and the measurements were being made over, say, 200 feet away.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: RTD Transmitter
We also minimize the types of signal types to eliminate a wide variety of home-run cables and associated junction boxes. Among the reasons that exist, some of the older and more primative DCS systems only accommodated low-level signals such as thermocouple and RTD's for open loops. The controller I/O required high-level 4-20 mA signals. Other DCS companies that were associated with large "batch" processes as well as most PLC companies had more variety for controller I/O than that popular primative DCS. Consider the direct RTD inputs where you have many temperature signals and few flow, pressure or other 4-20 mA signals.
RE: RTD Transmitter
I typically use RTD inputs direct when I have a lot of them in a single area. One example is in a pump bay (where you have say, 8 pumps side by each in close proximity) where you have temperature reading for winding, bearing, this and that.
I typically buy Rosemount transmitters. For temperature, they usually run about $1500.
Can you provide the make and model of the $120 US temperature transmitter?
"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
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RE: RTD Transmitter
There are few good reasons to pay that kind of money these days...
I googled for "temperature transmitter".
First one I found:
Scroll to very bottom. $235
http:
Second: Under $100
http://www.jumoplus.com/store/home.php?cat=337
Here's a page full from a 'not' inexpensive supplier.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: RTD Transmitter
Thank you for the links. Yes, these temperature transmitters are down in the hundreds of dollars.
The ones I was thinking of, are:
- field mount
- -40 - 40 °C ambient on all components
- Class 1 Div 1 Gr CD
- local indication
- NEMA 4x (IP 66/IP67)
- 3 and 4 wire RTD inputs
Different application I guess.
I guess I probably should have asked for a bit more detail.
"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
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RE: RTD Transmitter
Honeywell makes a transmitter for $115 us.
htt
RE: RTD Transmitter
Yes they do.
As you add in the ex-proof and NEMA 4X housing, local LCD, HART or Fieldbus, mounting, documentation etc, the price comes up from the $115 closer to $1000 +/-.
Thanks for the link though.
"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376: Eng-Tips.com Forum Policies to make the best use of Eng-Tips Forums?
RE: RTD Transmitter
RE: RTD Transmitter
Price varies, and I have been told, they have come down significantly since I last bought them. But to take a guess, I would say around $200 - $300 a card?
"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376: Eng-Tips.com Forum Policies to make the best use of Eng-Tips Forums?
RE: RTD Transmitter
RTD inputs cards are priced somewhere between $75-$150/point, depending on the class of PLC or process controller.
The four point SLC 500 RTD/resistance input card, cat # 1746-NR4, lists for somewhere around $900, but I think we've paid about $600 for it, at $150/point (several years ago)
A recent Honeywell HC-900 hybrid controller 8 channel universal card that takes eight, 3 wire RTD inputs was priced at $650, or $80/point.
Automation Direct's four channel RTD card, cat # F2-04RTD, (I've never used one) is priced at $300, at $75/point.
Dan
RE: RTD Transmitter
----------------------------------
Sometimes I wake up Grumpy.
Other times I just let her sleep!
RE: RTD Transmitter
But then I'm allowed to. I told myself I could.
However, for large comapnies you can bet your VP Purchasing has been out to dinner on on the glof course with the VP sales and Marketing of a Large multinational supplier who can do "single source" "One stop shop" etc. and they have signed a "Strategic Alliance".
You cost your job out with all sorts of good cheap products (i.e. cheaper and better than the Major companies offering) and try and get it past Purchasing.
Then you'll get it in the neck because your projected costs come in way under final costs when Purchasing (possibly without telling you) orders the equivalent from the single source supplier.
Now you just spend I hour looking for cheaper and better and you may find it. If this is a one off, you probably used up the cost savings through your time. Then again, they may not be an !approved vendor".
JMW
www.ViscoAnalyser.com