Raw min and Rawe Max values are for what?

[waterboy 7]

I'm using a 1771-IFE analog input module (on a PLC5) and the setup dialog shows "out of range" error when the Raw Min and Raw Max are zero. Where are those Raw values derived from and what purpose do they serve?? The data is all I am concerned with but should I be dealing with those other two values somehow? Is this a problem waiting to show itself somehow?

[Guest]

suppose that you’ve set up your IFE input channels to work with 4 to 20 mA signals ... setting the “Raw Min” value to 0 would tell the module: “when 4 mA comes in, I want you to report the number 0 to the PLC processor” ... likewise, setting the “Raw Max” value to 4095 would tell the module: “when 20 mA comes in, I want you to report the number 4095 to the PLC processor” ... suppose you are working with a water temperature transmitter that puts out 4 mA at 32 degrees F - and puts out 20 mA at 212 degrees F ... setting the “Raw Min” value to 32 would tell the module: “when 4 mA comes in, I want you to report the number 32 to the PLC processor” ... likewise, setting the “Raw Max” value to 212 would tell the module: “when 20 mA comes in, I want you to report the number 212 to the PLC processor” ... in other words, the IFE can do some basic scaling operations on the input signal - before the signal ever reaches the main PLC processor ... in practice, many (most?) experienced programmers go for the 0 to 4095 settings ... this approach gives us the maximum effective resolution (4096 steps) from our “12-bit” IFE input module ... if any additional scaling is required, it’s usually taken care of by programming math instructions in the ladder logic ... if you need more information than this, please tell us whether you’re using the 1771-IFE/A, 1771-IFE/B, or the 1771-IFE/C ... there are some differences - especially with the newer 1771-IFE/C modules ...

[waterboy 7]

I have tried replying twice and got SQL errors each time. I hope this one works I don't know the rev number I will have to drive there shortly to find out. I think you are saying that I should just enter those values in the setup box. If thats true then that brings another question . I have a module in another location that I tried to enter values into those boxes and they were constantly being overwritten. Is there a memory location or offset where those values get stored so I can see if I am overwriting them with something else? I attached a screen shot of the setup screen Edited 26 Oct 2006 by waterboy

[OZEE 5]

I believe you can program the raw min and raw max from either the PLC program or from an HMI. That could be what's overwriting them in that other program. We don't have access to the programs so can't tell you for certain. Regarding the RawMin and RawMax values, RawMax must be > RawMin. It CANNOT be < or =.

[bikerdude 0]

waterboy, to expand on what OZEE has provided, the actual min & max values are transfered from the PLC data table to the IFE modules memory via a block transfer instruction in the PLC's ladder logic program file. The block transfer normally only takes place during a power up sequence one time. If you can find this instruction in your program, look at the data table values (in Hex) that are being sent to the module. If you are using 4 -20ma inputs, then the min/max values should be 0 - 4095 for those channels. When editing the values on the screen that you have shown, the corosponding data tables in the PLC block transfer will be updated with the edits. They will not be sent along to the module until the block transfer instruction rung changes from false to true. Good luck BD