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Author Topic: Is This a RTD  (Read 4273 times)

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Offline shopteacher

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Is This a RTD
« on: April 25, 2004, 07:45:21 PM »
Pick this up at my favorite shopping emporium "Webster Salvage Yard" and want to know if this is one of the RTD we have talked about on the vac kiln thread. It's made by Rosemount,Minnesota.  Tag says its a 3044c temperature transmitter, supply 12.6-55 VDC. Output 4-20 mA. Calibrated 0 to 100 deg.C.  How many RTD's are needed? Is more better?






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Offline Den Socling

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Re: Is This a RTD
« Reply #1 on: April 25, 2004, 08:29:07 PM »
A transmitter changes the resistance of an RTD to a signal for something like one of Jason's PLC's. The one you got does the industry standard 4-20 mA. The connections that are shown in the bottom picture look like an RTD.

RTD's usually have three wires. Two have the same color. Those two, if checked with an ohmmeter will be near zero resistance. between either of those and the third wire, you should find 100+ ohms if it's the industry standard platinum 100.

RTD's have three connections so that the controller can tell how much resistance is added by the wires. That is why two go to the same place. It can then tell what the resistance is at the RTD's element. If the resistance is 114 ohms, for instance, the temperature is 97'F. if the resistance is 114.4 ohms, the temperature is 99'F and so on.

If the transmitter that you got doesn't work, I bet it has an RTD connected to it that does work.

Offline Den Socling

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Re: Is This a RTD
« Reply #2 on: April 25, 2004, 08:31:26 PM »
One RTD is needed. If you have more and they are connected through a rotary switch, you could make sure the charge is heating evenly.

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Re: Is This a RTD
« Reply #3 on: April 25, 2004, 08:42:18 PM »
There are 4 wires coming from the probe.  2 white and 2 red and connect to individual connections labeled 1,2,3,4. If this thing is good would it work with the controller to monitor the temperature in the wood? The stainless steel probe is 6" long and could be inserted into a board.  
 Inside the cap is a diagram of the 4 wires 2 each come off the resistance element inside the probe. There also a schematic I don't understand but below it it says" RTD w/comp loop.
Proud owner of a LT40HDSE25, Corley Circle mill, JD 450C, JD 8875, MF 1240E
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Offline Den Socling

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Re: Is This a RTD
« Reply #4 on: April 26, 2004, 10:52:40 AM »
4-wire RTD's are for highly accurate measurements. They have two wires going to each end of the element. Most controllers have three inputs for RTD's. Just connect 2 reds and 1 white or 2 whites and 1 red.

The RTD element is a little thing in the end of the SS probe. That's what I do, drill a hole and stick the probe into the wood.

Offline Fla._Deadheader

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Re: Is This a RTD
« Reply #5 on: April 26, 2004, 12:38:09 PM »
 You don'T use Drumsticks, like DanG ???  :D :D :D :D :D
All truth passes through three stages:
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   Third, it is accepted as self-evident.

-- Arthur Schopenhauer (1788-1860)

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Re: Is This a RTD
« Reply #6 on: April 26, 2004, 02:45:57 PM »
Nah, the drumbstick works fine, but the chicken tastes lousy after beeing in there.  Course I might be using the wrong type wood. I'll have to contact DanG for instructions on the proper methods of drying drumbsticks. ;D
Proud owner of a LT40HDSE25, Corley Circle mill, JD 450C, JD 8875, MF 1240E
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Offline oakiemac

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Re: Is This a RTD
« Reply #7 on: April 26, 2004, 04:56:34 PM »
Shopteacher, I believe you have a 4 wire RTD. to make it work, you'll need a 24vdc powersupply and some kind of readout(recorder, indicator, PLC) wired in series. You could just use an ampmeter in series with the loop but will probably need a 250 ohm resistor also. The meter will read 4ma at 0 degrees celsius and 20ma at 100 c. IF it doesn't, you are probably hosed, because that is a smart transmitter and will require a HART communicator to calibrate it. Some transmitters will have an external zero pot, but not all.

To find out of the RTD works, put it in an bucket of ice water then ohm out the leads. You should have 100 ohms between two of the wires and zero between the other two. I work with these things every day, so let me know if you have questions.
Mobile Demension sawmill, Bobcat 873 loader, 3 dry kilns and a long "to do" list.

Offline Fla._Deadheader

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Re: Is This a RTD
« Reply #8 on: April 26, 2004, 05:20:46 PM »
Oakiemac, you just screwed up. OH, there's gonna be LOTS of questions ::) ::) ;D :D :D :D
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-- Arthur Schopenhauer (1788-1860)

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Re: Is This a RTD
« Reply #9 on: April 30, 2004, 11:31:17 AM »
If this thing is good can I use it as is or do I need to remove the RTD and use it by itself? ???
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Offline Jason_WI

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Re: Is This a RTD
« Reply #10 on: April 30, 2004, 11:51:02 AM »
You are going to need a way to convert the 4 to 20 ma to something useful like F or C. From your picture, I didn't see any kind of electronics to do that.

Jason
Norwood LM2000, 20HP Honda, 3 bed extentions. Norwood Edgemate edger. Gehl 4835SXT

Offline oakiemac

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Re: Is This a RTD
« Reply #11 on: April 30, 2004, 04:45:03 PM »
To use that transmitter you are going to need a 24vdc power supply and some sort of indicator. You can use an ampmeter but you will need to do some math to convert.
If you are serious about using that Rosemount, let me know and I can fax you a drawing.
Mobile Demension sawmill, Bobcat 873 loader, 3 dry kilns and a long "to do" list.

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Re: Is This a RTD
« Reply #12 on: April 30, 2004, 05:44:20 PM »
Oakiemac: I haven't  figured out yet if it will work. I thought Den said the RTD would be connected to the controller. Can this Rosemont be connected to the controller to tell it when the wood is at a certain temp so the vac. could be started or turned off.  Or do I have to take the probe and 4 wires out of the rosemont and connect it to the controller and use it as an RTD that way?  
  Got a line on a tank, haven't seen it yet so don't know if it will suit the situation or not, soundings promising though.
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Offline Den Socling

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Re: Is This a RTD
« Reply #13 on: April 30, 2004, 05:46:28 PM »
Or just take the RTD out of the transmitter, connect it to a loop controller and tell the controller to read an RTD.

If, for some reason, you want to use the transmitter, they will usually run with a wide range of excitation voltage. Some will work with anything from 9 to 40VDC. I've seen some cheap setups that used DC adapters instead of a decent DC supply. If you use it as a transmitter, you have to scale engineering units in your display to get the correct readout.

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Re: Is This a RTD
« Reply #14 on: April 30, 2004, 06:53:11 PM »
Den, depends on the controller. Some will only take a 4-20ma signal, some will take a T/C or RTD input.
What kind of controller do you have shopteacher? If you are turning pumps on and off, it sounds like you need a logic controler or PLC.
Mobile Demension sawmill, Bobcat 873 loader, 3 dry kilns and a long "to do" list.

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Re: Is This a RTD
« Reply #15 on: April 30, 2004, 07:25:22 PM »
I don't have any controller yet. Just gathering parts and trying to figure what will work.
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Re: Is This a RTD
« Reply #16 on: May 01, 2004, 07:18:25 PM »
OK, found this today in some of my junk. What is it and will it do me any good if it works?




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Offline Den Socling

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Re: Is This a RTD
« Reply #17 on: May 01, 2004, 08:26:55 PM »
It looks like a transmitter that can do either thermocouple or RTD input. Where do you get this good junk?  ???

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Re: Is This a RTD
« Reply #18 on: May 01, 2004, 08:38:44 PM »
Why from the good junk yard naturally ;D
Proud owner of a LT40HDSE25, Corley Circle mill, JD 450C, JD 8875, MF 1240E
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Re: Is This a RTD
« Reply #19 on: May 03, 2004, 06:56:47 AM »
Den is correct. It is another temp. transmitter, same as the rosemount just a different manufacturer. It should put out a 4-20ma current signal in porportion to the range of the transmitter.
Mobile Demension sawmill, Bobcat 873 loader, 3 dry kilns and a long "to do" list.

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Re: Is This a RTD
« Reply #20 on: May 03, 2004, 08:45:09 AM »
I can't seem to get this straight. Will this only show the temperature or will it show the temp( on the display )and also act like a household thermostat and turn on and off a device, for instance the vac pump like the Tstats controls the furnace?

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Tilt Bed Truck  and well equipted wood shop.

Offline Den Socling

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Re: Is This a RTD
« Reply #21 on: May 03, 2004, 09:09:40 AM »
A transmitter transmits the signal from a transducer. I don't know what the display does but the device doesn't look like a controller. A controller would have a relay, current or voltage output that responds to a setpoint and a process value.


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Re: Is This a RTD
« Reply #22 on: May 04, 2004, 06:53:28 AM »
Sorry shopteacher, but those transmitters won't turn a pump on and off by themselves. They will show the temp and also put out a signal (4-20ma). If the transmitter is ranged for 0 thru 100 degrees, then at 0 it would put out 4ma, at 50 degrees or 50% it puts out 12ma, and 100 degrees or 100% it puts out 20ma.
You can get trip units which you can set to say trip at 50%. Then when your RTD is a 50 degrees it will close a set of contacts that you could wire to trip a larger current relay that in turn would turn your pump on. Then your transmitter and trip unit would work as a loop and serve the same function as a house thermostat and give you on/off control of the pump.
Mobile Demension sawmill, Bobcat 873 loader, 3 dry kilns and a long "to do" list.


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