Internet PLC Forum

If you wire the DA3 and DA4 (for FMD PLCs) to GND then as long as you don't turn on the DA3 and DA4 outputs they should not have effect on your ADC readings. But if for some reason the program runs the SETDAC on channel 3 or 4 you can cause a short circuit to the DAC output and that can affect the 5V reference voltage so we recommend that you do not connect them to 0V.

We found that in most cases the screen number is visible in the screen properties below the screen name. However, the screen number will not be displayed in screens used by tasks such as "Goto Screen Number x"

It appears that some screens still don't show the screen number even though there is no apparent task interacting with it, so we are investigating this further to see if there are other reasons that the screen number would not be visible.

It is possible to duplicate screens, which will create an exact copy of the screen in the next available slot. You can do this by right-clicking on the screen name in the "Screens" directory.

The duplicate screen will have a new number corresponding to the available slot and a default name. Both of these properties can be changed after. If you are unable to delete the original screen (with the intention of reinserting the duplicate screen after), then you can leave it unused and switch any task interactions to the duplicate screen. Both the original screen and duplicate screen can be renamed such that the duplicate screen takes the name of the original screen since it is now being used in your program.

We are looking into this and will provide a reply as soon as possible.

AWESOME!

Thanks for the contribution, Gary. We appreciate it!

Thank you Gary. That is a great response.

Ondercin, a few other notes of importance.

1) On the FMD88-10, ADC #1-6 are high impedance with no internal pull down resistors, whereas ADC #7-8 are pulled down to 0V via on-board 20k resistors.

2) Since ADC channels 1-6 are all high impedance, they will float high when disconnected. In order to reduce the effects of electrical noise, we recommend that you connect any of these unused inputs to common (0V).

3) Since ADC channels 7-8 are internally pulled down via 20k resistors, you will need to follow the recommended resistor wiring in section 5.2.2 of the FMD88-10 user manual when interfacing to 4-20mA analog sensor signals. I would recommend using any of channels 1-6 instead so that the resistor wiring is simplified.

4) If you follow Gary's recommendation to use 0-10V sensor outputs, then it will be easier to use ADC #7-8 for the voltage divider since you only need to add a 20k resistor in series with each of the two ADC inputs. You would then need to add a full 2 resistor voltage divider for the 3rd sensor that would connect to any of ADC #1-6 since these do not have any internal pull down resistor.

5) Adding software filtering is highly recommended. If you want to apply some simple software filtering first, you can use the following to take the average of 100 readings on each ADC channel you are using.

-----------------------------
FOR I = 5 TO 7
  A = 0
  FOR J = 1 TO 100
    A = A + ADC(I)
  NEXT

  DM = A/100
NEXT
-----------------------------

This will store the averaged ADC readings in DM[5] to DM[7] corresponding to ADC(5) to ADC(7). The above code takes about 35ms to execute, so there is plenty of time to take new averaged readings every 100ms (assuming the rest of your program is not overly large and doesn't contain delay statements).

I'm sure Gary's software will provide more sophistication, but the above code will help a lot.

You have to edit the file 0.htm using a text editor (download Notepad++ if you don't have one. It is a great editor), then upload the updated file to the PLC's webserver using FTP client such as the FileZilla.

From your outcomm pattern error it appears that when the error occured, the RS485 transmitter transmitter was switch off prematurely during the transmission of the last byte so the 2 MSB became a '1' when they were supposed to be zero.

Can you check the firmware version of the PLC that was involved (both masters and slaves)?  Have you upgraded their firmware to the latest version? There were some changes in the firmware relating to RS485 transmitter timing in recent firmware fixes that aim to improve RS485 communication and a firmware upgrade may eliminate the problem. If you don't have the firmware upgrade link please write to support@triplc.com for more information.

Do have have a terminal emulator software? The RealTerm software (free download) can be used together with the U-485 to see the data that flows on the RS485 bus. As per Gary's suggestion, remove all the other devices on the rS485 bus and then just use the OUTCOMM command to send data from your program and check what the terminal emulator software see to confirm if the wrong data byte  actually comes from the PLC.

If without other devices attached and the OUTCOMM seem to work properly with the proper data output but the data get corrupted when the other devices are attached then someone is driving the RS485 bus when it is not supposed to and that could lead to corruption of the data from the PLC.