FX3UC - Writing to outputs

[Hess]

I have been given the task of adding some functionality to an already existing system. Basically I need to directly write some input data (2 actuator positions) to two outputs for an external data logger. Might seem counter intuitive but that's the task. Now I have had no proper training in ladder logic or PLCs but have picked up some aspects of it over the last few months. I have an FX3UC-64MT, with inputs from 2 FX3u-4AD-ADP 's and outputs to 2 FX2NC-4DA 's. The inputs are 4-20ma signals and the outputs are 0-10V. This part is pretty easy. The existing logic already reads the inputs and uses them fine, so I just need to copy this information across to the output pins. My first output module is full, so I am using the second one, of which a single output of the 4 available is being used. Therefore I want to use outputs 5 and 6. This is the line of ladder logic I have added. I'm pretty sure it's wrong in at least one location and could possibly be completely wrong altogether. If anyone has any idea what I'm on about and can help I would be very grateful.

[JRoss]

You're on the right track. If you haven't already, you should download the Analog Edition FX3U Programming Manual (JY997D16701-J) and the FX2NC-4DA user manual (JY997D07601-C) from the Mitsubishi website (www.meau.com in the US, if you can't find it on the European site). These will have information and sample programs for the FX analog modules. First, you'll need to make sure the output card is configured properly for 0-10 by writing the correct values to the correct buffer memory locations on the card. The input card is working, so should already be done. This is really where the manual is invaluable. In the output card manual, look Second, you'll need to scale the value from the input card before passing it to the output card. Look at the specifications section of the manual for each card, and it will show you the digital values that correspond to the analog values. The FX3U-4AD-ADP set to 4-20mA has the range 0-1600, while the FX2NC-4DA set to 0-10V has the range 0-2000. Finally you're ready to pass the value across and have it work as expected. For the first and third steps above, you'll need to use the TO instruction, as you've already discovered. This instruction is only necessary for right-side bus Special Function Modules (SFM) like your output cards. Let me deconstruct the instruction for you so you know how to set it up: Argument 1 - This is the head address of the module. Essentially the position of the card, ignoring all digital I/O expansion cards. The FX allows up to 8 SFM, so this will always be in the range 0-7. Since you say this is the second analog output card, and assuming that you don't have any other SFM before it, then you've correctly entered "K1". Argument 2 - This is the buffer memory location of the information you are moving on the SFM (for the TO instruction, this is the destination). Looking at the manual, you want to put your information into the "Output Data Ch1" which is buffer memory #1, so this argument should be "K1". Argument 3 - This is the register on the PLC (for the TO instruction, this is the source). You have put in D8270, which is the special register that stores the input data from your input card. However as I've already noted you need to scale this, or you won't be using your whole 0-10V range. So do some math and put the result register here. Argument 4 - This is the number of registers to move. The TO instruction is a block move, so you can move more that one register at a time. This is a time savings, as the backplane communications can be slow, though it's only a problem on high-speed applications. Regardless, you can either put in "K1" to just move one channel of data, or you can put in "K2" to move both channels, just make sure the source data is in adjacent registers. Hope that helps.