CliveC Posted November 22, 2011 Report Share Posted November 22, 2011 Hey, I am new to this programming/hardware environment and I am struggling to get my head around how to get a PT100 temperature gauge to work? The PT100 I am using consists of 2 leads, and I am using the V350-35-TRA22. I have changed the jumper settings according to the manual, and setup the inputs in my hardware configuration, however when trying to access the value via a HMI screen, it outputs 32767, saying the sensor is not found? Is there something that I am missing out?? Any helps or pointers would be appreciated, Thanks! Link to comment Share on other sites More sharing options...
MVP 2023 Joe Tauser Posted November 22, 2011 MVP 2023 Report Share Posted November 22, 2011 Most PT100 sensors have three leads, and that's what the Unitronics input is designed for. Are you sure you don't have a thermocouple? Are the leads different colors? If you measure between the leads with an ohmmeter, do you get some value above 100 ohms or do you get a dead short? Joe T. Link to comment Share on other sites More sharing options...
AlexUT Posted November 23, 2011 Report Share Posted November 23, 2011 Hi Clive, To get the most accurate measurement we highly recommend to use 3-4 wire RTD sensor. Using 2 wire sensor may lead to very unstable (sensitive to noises) and un-precise (affected by wire impedance) reading. If anyway you have two wire RTD sensor, you need to connect one of the wires to T+ and T- (both have PT label as well) and the second wire connect to CM. You need to define selected input as PT100 in hardware configuration in accordance to used PT100 type (alpha=0.0385 or, alpha=0.0392) assign MI and select C(celsius) or F. Then you will see in assigned MI raw number, which is 10xt. Example: you see raw number 247. Temperature is 24.7 C. When MI = 32767 Sensor is not connected to input, or value exceeds permissible range, or sensor is different than PT100 (for example, PT1000). When MI = -32767 Sensor is short-circuited Link to comment Share on other sites More sharing options...
Walkerok Posted November 23, 2011 Report Share Posted November 23, 2011 I am curious, I have used 2 wire 1000 Ohm RTDs for about 12 years and have never had a problem with noise (that I am aware of). I have not used an RTD with a Unitronics, but is there any test data that anyone knows of that would show me the relative affect of having a 3 wire RTD over a 2 wire RTD in similar noisy environments. Or is it simply a matter of accuracy in that a 3 wire is more accurate than a 2 wire in all conditions. I know that the 2 wire units we use have always had better accuracy and much lower noise that any thermocouple I have ever used which is why we went that way in the first place. It is completely accidental that I have allways used 2 wire units, it is just what was selected from a companey that has a very inexpensive converter from 1000 Ohm RTD to 4-20ma that we needed at the time and we have never altered what we are doing with that product. Thanks Keith Link to comment Share on other sites More sharing options...
MVP 2023 Joe Tauser Posted November 23, 2011 MVP 2023 Report Share Posted November 23, 2011 Keith- A 1000 ohm RTD is typically two wire because the ohm or so of lead resistance has a small (< 0.1%) effect on the temperature reading. A three wire 100 ohm RTD is much more common and allows accurate resolution of 0.1 degree but obviously lead resistance becomes an issue. The third wire is used in an adaptation of a 4-wire ohmmeter to actually measure the lead resistance and subtract it from the RTD resistance. Joe T. 1 Link to comment Share on other sites More sharing options...
MVP 2014 Simon Posted November 23, 2011 MVP 2014 Report Share Posted November 23, 2011 Along with Joe's post, the main use of the 3rd (or 4th) wires is to compensate for wire resistance. I suppose it could also eliminate noise if the noise was affecting the main sensor wires as well as the compensation wire, so the noise was then cancelled out. If you only have a 2-wire probe and the interface expects 3 or 4 wires, you can trick the interface by bridging the compensation terminal to one of the RTD terminals locally at the interface. This of course defeats the purpose of compensation, but at least allows the interface to operate. If the resulting accuracy is sufficient for the application, then you have achieved your purpose. Take a close look at the Unitronics wiring diagrams when doing this, as wiring errors are a common reason for non-functioning RTDs. Link to comment Share on other sites More sharing options...
denci Posted November 28, 2016 Report Share Posted November 28, 2016 I am using Unitronic Samba SM35-J-RA22 and pt100 temperature sensor. I confugered sensor as pt100 analog input on MI0 and when i want to read temperature from sensor i alwayg get value 32767, what i am doing wrong with temp reading?? Link to comment Share on other sites More sharing options...
denci Posted November 29, 2016 Report Share Posted November 29, 2016 I have double checked my connection of pt100 and seems right regarding plc manual, so I don't know what else should be wrong there. Link to comment Share on other sites More sharing options...
Isakovic Posted November 29, 2016 Report Share Posted November 29, 2016 13 hours ago, denci said: I am using Unitronic Samba SM35-J-RA22 and pt100 temperature sensor. I confugered sensor as pt100 analog input on MI0 and when i want to read temperature from sensor i alwayg get value 32767, what i am doing wrong with temp reading?? When you measure Pt100 resistance it should be around 120 ohms or so. 32767 means you are out of range and you have open circuit between points where PLC measures resistance. Either your probe is faulty or it is a wiring error, which is more probable. Link to comment Share on other sites More sharing options...
denci Posted November 29, 2016 Report Share Posted November 29, 2016 I have double checked connection and measure resistance of PT100 and all seems perfect but plc still show value 32767. Maybe something wrong with setting of analog input of plc, maybe there is some trick to configure analog input. I read many description how to configure pt100 and I have no idea what is wrong. Maybe problem is because I am using 2 wire sensor and bridged one wire to second connection sensor with other wire (one wire of pt100 is connected on CM pin). Link to comment Share on other sites More sharing options...
Cam Posted November 29, 2016 Report Share Posted November 29, 2016 Which set of inputs did you connect to ? Sensor 0 would use inputs 9 and 10 in reference to CM on input 11 Sensor 1 would use inputs 7 and 8 in reference to CM on input 11 I've set this wrong before thinking 7 and 8 are 0 and 9 and 10 were 1. Also double check your jumper settings http://unitronicsplc.com/wp-content/uploads/2015/12/SM35_43_70_RA22_IG_2_16.pdf Link to comment Share on other sites More sharing options...
Daniela Posted July 29 Report Share Posted July 29 Hey @denci did you solve this problem? Now I'm learning this on SM43-J-TA22 plc and everything is connected properly. I chose Pt100 from the analog inputs 1(because the 2 wired sensor is connected to CM with the first wire and to I7 and I8 with the second wire) in HW configuration panel and I addressed it to MI0 and then I put Number panel on the display and liked it to MI0 and of course I get 32767 :))) Link to comment Share on other sites More sharing options...
AlexUT Posted July 29 Report Share Posted July 29 There is a Jumper you have to change position. This jumper allocate CM instead of DI. . Link to comment Share on other sites More sharing options...
Daniela Posted July 30 Report Share Posted July 30 @AlexUT It works!! You're amazing, thank you. Link to comment Share on other sites More sharing options...
MVP 2023 Ausman Posted July 30 MVP 2023 Report Share Posted July 30 Page 6 of this guide: https://www.unitronicsplc.com/wp-content/uploads/2015/12/SM35_43_70_TA22_IG_2_16.pdf PLC 101....read all manuals for any PLC before doing anything! Most importantly, anything relating to connections. Otherwise you might destroy some circuitry, or even worse, the entire unit. 😉 Link to comment Share on other sites More sharing options...
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