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Analog voltage output problem

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  • Analog voltage output problem

    just discovered that DL205 analog voltage output F2-08DA-2 which has been working well before is now giving only max 3,0V output. I has been 10V before and I can't remember to have changed anything that could affect the voltage. Monitoring output memory and manually adjusting it up to 4095 gives only 3,0V. It seems to work nicely proportional from 0 to 3V when changing input values. External power supply gives 24,3V to the module so it should be ok.

    Any ideas where I should start tracking the problem? It's a bit complicated wiring with 2pcs of 9 slot bases in series in a very small space so it's not easy to start disassembling anything from the system or changing some modules just for testing. One thing I already tested and found out that a similar module in the second base gives output of 10V.

    Any ideas or proposals?

  • #2
    okay, more testing...
    - Other analog modules on the same base are giving up to 10V, so they're working ok
    - This particular module actually gave 3,5V last time I measured it
    - I measured couple of the output terminals in this module and they all gave 3,5V output.
    - I already uploaded a program with END statement at the beginning to rule out possibility in program error. Then manually changed the value.

    Seems it might be problem in the module itself or some cabling (supply) problem though measured between module supply terminals it was 24,3V. Problem in the module sounds a bit strange as it seems to reach proportional to input value, only the scale is incorrect.


    • #3
      Check the devices that the module is wired to. The minimum resistance that module can drive is 10kohm @ 10VDC. If it is only giving 3.5V when unwired, then it has probably toasted the drive circuit trying to push too big of a load (possible short, etc).
      If you have an urgent issue, please contact AutomationDirect's Technical Support team. Technical Support: 1(800) 633-0405 or (770) 844-4200 Email Tech Support


      • #4
        Thanks, need to start figuring that out. It's been wired to light dimming transformers, don't know the resistance. Same way than couple of other voltage output modules are also in this system. Of course it's possible it has had some kind of short circuit but it has been working properly for couple of years.

        Voltage seems to be travelling a bit... last measurement was 3,7V at full output and after couple of hours 4,0V... gradually rising.
        Last edited by makkis; 10-13-2014, 03:46 PM.


        • #5
          Hi, just toasted another F2-08DA-2...

          - 2 months ago replaced the first failed module and it's been working fine since that
          - now the second one had just same behaviour than the first one toasted
          -> at first the output vibrated sometimes
          -> later it started to fade out, output voltage gradually lowered and was unstable

          Made some measurements for the dimmer device that are wired to the second failed device
          - Dimmer inputs have ~10V "counter" voltage which means output module sinks the current from dimmer when module's output is lower thank 10V.
          -0,35mA @ 0V
          0,00mA @ 9,5V
          +0,05mA @ 10V

          I couldn't fine any information about F2-08DA-2 current capabilities. Only that 10kohm @ 10V which would mean max 1mA current. Is it ok sourcing and also sinking?

          I also have max of 3 dimmers connected parallel on one output channel. That of course means the 0V sinkin current would probably be a bit too high.

          Now I don't know what would be the way to resolve this. I know that without any changes in wiring these modules work ~1,5 years (I have 4 of these modules in use in the system). Without any further information or suggestions I could think about adding an extra resistor on each channel and accept the loss in control voltage.

          Any ideas? Thanks!


          • #6
            Don't think the modules will like sinking current. You might need to put isolators in between so the information can flow without a direct electrical connection.


            • #7
              Do you have a link to the specifics of these dimmer devices?



              • #8
                Isolators would be a solution but it's a bit expensive... would be nice to come up with a cheaper solution.

                I don't have any proper specs available, this kind of specs only:


                Model SR-2002
                This is one of the two dimmer types I have in use.


                • #9
                  Here's a link a little closer to the supplier but still not much information about internals or specific wiring diagram.

                  Given this image can you detail exactly how you are wired (power and signals) from the analog output module to the dimmer?

                  I'm not sure about the 'T' symbol associated with the analog inputs. Is it just the common point for these 4 circuits? Maybe you can measure the input impedence. The instructions talk about a 'standard' input but I wonder if that is different than what we are assuming.
                  Last edited by bcarlton; 01-06-2015, 03:45 PM.



                  • #10
                    If one were to Google;
                    1-10v dimmer buffer
                    one would find lots of information, unfortunately most of it not quite applicable. I think a good starting point would be one of the circuits designed to be driven by an arduino. e.g.

                    "An op-amp is capable of sourcing and sinking so it will work as a "buffer" as you require. I think you want something like this:"

                    You wouldn't need the low pass filtering used for PWM, but the op amp buffer should make your output module happier.
                    I have no idea where to get such a circuit "off the shelf", while 1-10V (or 0-10) is a industry standard thing, it seems it is usually used with industry standard dedicated controllers, not general purpose PLCs. I suspect a buffer may have to be a DIY project.


                    • #11

                      thanks for your replies and sorry for delayed answer.

                      1. From the analog output module the 0V connects to dimmer signal input ground.
                      2. Analog output channels (V1-V4) connected to dimmer signal inputs (1-4).
                      3. Analog output module 0V and 24V connected to separate 24VDC source.
                      4. Dimmer input + and - connected to another separate 24VDC source.
                      5. Led loads connected to dimmer outputs.

                      Tinker, thanks for the advice. Probably op amp voltage follower would be a solution for this. Didn't find any reasonable products for this purpose so probably I need to get op ams and do some welding myself. Need to get into it a bit more, haven't done op amp circuits before myself.


                      • #12

                        back then couple of months ago I actualised the op-amp plan. I built a simple voltage buffer (voltage follower) for each output in the analog module. It's now been running for couple of months and seems to be working as expected and was simple to build.

                        Op-amp sinks the current from active dimmer and also sinks output current from analog module. Now current directions should be as required. Let's see if it works in long run.

                        Thanks for advices!


                        • #13
                          If you want your PLC to handle linear proportional control of a lot of resistive load current then you want to look at these linear proportional controllers devices. These devices can handle up to 110 Amps resistive load. Take a look at the data sheet.
                          For use with resistive loads only!

                          I'm not affiliated or promoting this device. It's something I came across.
                          Last edited by LWgreys; 04-13-2015, 07:56 PM.


                          • #14
                            you could use arduino plc industrialshields

                            Hello, for theses aplications, you could use Industrial shields plc. or not?
                            these equipments use an Arduino board. IndustrialShields is really simple because you can programm it with arduino IDE.