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Showing content with the highest reputation on 05/30/2019 in all areas

  1. 2 points
    There are a couple of I/O module that can you can directly connect a 100 ohm RTD to - the V200-18-E3XB snaps onto the back of the V700 and the IO-PT400 expansion module is similar to the IO-ATC8. Both of these modules return the temperature directly in 0.1 degree units, which probably what's confusing you. But this is not what you have in the Prosense (translation: Evil Empire) transmitter. You need to understand what you'll be feeding the IO-ATC8 electrically from the transmitter. It's not ohms. Let's lay it out: 0 F = 4 mA 300 F = 20 mA The IO-ATC8 is an A/D (analog to digital) converter that produces a number to the PLC based on it's input. You said you understand it's 14 bit, but do you know what that means? Let's lay that out, too: 0 mA = 0 counts to PLC 20 mA = all 14 bits on = 2^14 = 16384 counts to the PLC So your transmitter starts at 4 mA. This means at 0 F the IO module will return (4/20*16384) = 3276.8 counts, which it will round to 3277. At 300 F it will return 16384 counts. Read the Help on the LINEAR block, which includes some fun diagrams under the subtopic "Linearizing Analog I/O Values" So you set your linear block up like this: X1 = 3277 (point 1 input) Y1 = 0 (point 1 output) X2 = 16384 (point 2 input) Y2 = 300 (point 2 output) Map X to the register assigned to the channel on your IO module and Y to whatever MI you want to use for the output. If you still need help post your program. Joe T.
  2. 1 point
    And the final follow-on to all of this number talk. At first glance the calculator is a useful thing just to get your head around how Linearisation works. But it does have a "higher purpose" and that's why I did it. In the theoretical world, all 4-20 sensors work perfectly on those numbers mentioned. But in the real world, sensors, the plc's input or both can be slightly off. If it is a simple linear difference over the entire span, then a + or - amount to the result is all that is needed to get complete accuracy. However, if the span itself has some innate error, the calculator lets you play with numbers very easily to get the best match to adjust things. In all the sensors I use, many of my linearisations are NOT set at the numbers above, they have small variations to correct for this error. My "need no adjustment at all" percentage is probably 25% of the sensors in use. How critical your reading needs to be is an important factor in whether to play with this or not. In my case I have to have all temperature sensors perfectly matched to a master device, otherwise I can get control conflicts. In other situations this is not strictly necessary. cheers, Aus
  3. 1 point
    Ah, sorry, I misunderstood.
  4. 1 point
    I always tell my guys that get confused, "to a computer, zero is a much a number as one is, only people think zero means nothing"
  5. 1 point
    It's 16383. There are 2^14 counts, but it starts at zero, so the highest number is 2^14-1 (all 14 bits on would be 2^14-1, or 16383). This is what goes into your linearization block, though you would likely never notice it in the real world if your linearization was off by 1 part in 16384.
  6. 1 point
    As I was writing my answer, Joe's has popped up and says it all. One thing I might add is to go this topic and get the calculator, which might help you understand some of the principles a little easier. cheers, Aus
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