cFP RTD 122 Temperature error

[swam]

I have a cFP 1804  controller with two temperature modules and one analog and one strain Guage Module. When I hook up my RTDs to the modules the temperature shows me 850 degrees under MAX and the STATUS shows that its an Open RTD but when I change the channel settings from -200 to 850 degrees to 0 to 4000 ohms resistance in MAX then it gives me the exact resistance values as measured and the STATUS gives me successful. Why is this that when trying to get the temperature it gives me this error ..........? any help would be great.

Thanks
sunswam

[NathanT]

Sunswam,
       What sort of RTDs are you using?  Does it have 2,3, or 4 wires?  How does it perform with the other resistance and temperature ranges?  Can you please double check the manual's wiring diagrams to make sure that the RTD is connected correctly?

Thanks,

Nathan

[swam]

Hello Nathan,
          Sorry I have a YSI 400 series thermistor which I am using in an RTD module cFP-122 to measure the temperature. Please let me know if this has to be converted to temperature or if temperature can be measured directly. Its a two wire. I have connected according to the manual instructions.
Thanks

Sunswam

[NathanT]

Sunswarm,
       Thanks for letting me know what kind of RTD that you are using.  Are your leads about the same length?  Or is one a lot longer than the other one?  Try wiring a regular resistor in the 2 wire method and testing the resistance.  How are your other modules working?  What happens on other channels of the RTD module?  Do you have any three or four wire RTDs to try? 

Looking at page 7 of the RTD-122 user manual, it seems that the RTD-122 can only directly measure temperature of PT100 or PT1000 RTDs.  What is the nominal resistance of the YSI 400 series?  Is it 400 Ohms, if it is, I think you will have to do the temperature calculations after taking the resistance.

Thanks,

NathanT

p.s. Here is a link to the user manual

[swam]

Hi Nathan,
 sorry for the late reply. My leads are of same length. Actually these are for medical purposes measuring blood and body temperature. So they are needle probes or catheters. They are interfaced thru an extension cable to go to the original monitors. I bought the same cables from the manufacturer and made a pig tail and           (2 wire ) and hooked them to the Modules. I dont have any 3 wire or 4 wire RTDs. Currently I am testing only two channels both of them work fine showing the resistance values. the nominal resistance is 400ohms . So looks like I need to use the resistance Temperature chart to convert to Temperature.

Any help in making a good resistance temperature converting program would be great. I have the cahrt the Manufacturer provided us. I will use the same table to program it. Any suggestions or examples would be nice as the table does not account for very accurate temperature measurement could you show me any examples of them?

Thanks
Sunswam

[NathanT]

Sunswarm,
      I recommend taking a look at Working with Thermistors and RTD's  and then "What Are Custom Scales, and How do I Use Them?".  You can create a task in Measurement and Automation Explorer and then create a custom scale for it based on the table that the RTD manufacturer provided you.  Let us know how it goes.

Cheers,

NathanT

[NathanT]

Sunswarm,
       I just remembered that you were using a Compact FieldPoint and not a data acquisition device supported by DAQmx.  You will need to do your scaling either in LabVIEW or Measurement and Automation Explorer.  Please take a look at "Can I Scale FieldPoint Channels in MAX?" , but be aware that it only does linear scaling, so you will probably be better off doing the scaling in LabVIEW.  Please let me know if you have anymore questions.

Thanks,

NathanT

Message Edited by NathanT on 10-10-2006 10:47 PM

[swam]

Hi Nathan,
 Thanks for you info. It was greatly helpful in proceeding forward I made a big leap. I got everything set and I used the steinhart to measure temp. It s wroking real great. But the cFP 122 does not allow to measure resistance greater than 4000 ohms. I vaguely remember that can be done by connecting resistors in the module. How do I connect them in the module and what resistor values should I use? I need to measure till atleast 15Kohms around -5 deg C. What value resistor should I use in order to increase my range from 0 to 4000ohms to 0 to 15Kohms do you have a formula or a info that you could provide. right now I am able to measure upto 4000 ohms which is around12 deg C. I need to increase my range.

Also I have an analog Input Module. its AI 110 it does not measure any voltage. I am measuring flow thru  analog out (BNC) two wire. I connected. V in and ground. it does not have supply voltage. So my Vsuuply is not connected. I am troubleshooting this one too. when I measure in ordinary PCMCIA 6023. it gives me exact values. But in cFP nothing shows up . Any suggestions?

Thanks
sunswam

[Steven_T]

Hello Sunswam,

That is a really interesting question.  Here is a knowledgebase that allows you to lower the resistance by adding a parallel resistor.  It also lists the equiation which is 1/Re = 1/R1 + 1/R2.

http://digital.ni.com/public.nsf/websearch/C200644052C8BD5B86256CB8005A24D1?OpenDocument

Anytime you are noticing strange behavior in FieldPoint, make sure that the same results happen in Measurement and Automation Explorer.  What voltages is it measuring instead?  Can you short the voltage in with the ground and get 0 Voltes? 

I hope this helps,
Steven T.

[swam]

Hi steven,
     When I hook the AI from tye BNC to the cFP Analog Input Module. I recieve 0 Volts and there is no change in it. I dont know the reason why it behaves I tried switching the wires and changing channels. This happens in MAX and since I dont see anything in MAX I have not yet proceeded to the program. Any possible reason. but When I hook up the same AI to PCMCIA card 6023E i measure the correct voltage.

Thanks
Sundar