1762-IF4 Questions

crono141 · Jul 30, 2018

Hey All,

I'm still pretty new to PLC programming, and in particular how to translate Allen Bradley's documentation into real world information.

The 1762-IF4 Analog to Digital converter has a input voltage range of -10V to +10V, and a 15 bit (bipolar) resolution. I'm trying to figure out what this means. 15 bit resolution means 0-32768. So does that mean -10V equals 0? Does -10V equal -32768, or does -10V mean -16384 (with +10V meaning +16384).

I'm having calibration issues with 2 sensors connected to this ADC, because I'm not sure how I should be scaling the input. Please help! Thanks.

Data sheet here: https://elebi.com/wp-content/upload...y/MicroLogix 1762-IF4 Analog Input Module.pdf

bright676 · Jul 30, 2018

Scale it to what type of sensor you are using, most are 4-20ma

crono141 · Jul 30, 2018

I have a 1V-5V sensor. The problem is I don't know what value to set 1V to (3277 or 1638), and likewise, I don't know what to set 5V to (16384 or 8192). If 1V is 3277 then 5V should be 16384 (which is what I'm currently using). However, with these values I cannot get a sensor to calibrate. We've maxed out its calibration potentiometer and are still short of the target value. If I change the 1V to 1638 we can calibrate, but then I should change the max to 8192 (since its a 10V ADC, and I'm only using 5V of it). Doing that would cause the reported values to be way over actuals.

roxusa · Jul 30, 2018

Are you measuring 1v-5v off this sensor. If so adding any length of wire from sensor to PLC will change your readings, as bright676 mentioned most sensors are 4-20ma
Iv'e used 0-10 vdc in the past but prefer 4-20ma because of the repeatability of the scale factor even with different lengths of cable. 1v-5v seems like a poor range for a sensor

roxusa · Jul 30, 2018

Run it through the SCP function block and scale it accordingly, Turn it down all the way a read what you have - then back up use these numbers for your min/max input and then scale with what you want

crono141 · Jul 30, 2018

Thanks. We are using the EWS-RH Temperature Humidity Sensor, wired in the 1-5V mode. Its potentiometers do not allow the output to scale from 1-5, its just an adjustment, so I can't zero and then max the output to see what we get on the ADC. I am using the SCP function to scale the output to real numbers, just don't know what real numbers to use. The manual for the ADC is unclear.

https://www.omega.com/manuals/manualpdf/M3501.pdf

roxusa · Jul 30, 2018

that sensor is user selectable 4-20ma or 1v-5v

crono141 · Jul 30, 2018

Yes, but it is currently wired to 1-5, and the ADC is set to 1-5, and the product is 800 miles away and I can't get to it to rewire it. All I can do is update the connected PLCs program.

roxusa · Jul 30, 2018

What pot are they maxed out on: P1 is the low end and P2 is the high end, book says never touch P3

roxusa · Jul 30, 2018

I think your original numbers were correct 3277 min & 16383 max if it was calibrated correct. are you reading both humidity and temperature

crono141 · Jul 30, 2018

We have only adjusted P4. When we crank it all the way it does not reach a value that correlates with a second Fluke temperature probe. It needs to go up 3 more degrees F. This is what makes me think there is something wrong with my program scaling, because we ran into this problem with a brand new sensor from the factory (Read 10F low out of the box).

roxusa · Jul 30, 2018

Good luck, Data sheet shows _+ 1.2-3F but your over that

crono141 · Jul 30, 2018

Thanks. I was hoping someone with experience on this ADC would have clued me in to whether I was on the right track. If need be (because of long wire) I can add a correction factor to this sensors output, but before I do that I want to make sure that I have the input scaled properly.

JaxGTO · Jul 30, 2018

The AB tech article 19719 (access everyone) has the scaling for each mode.https://rockwellautomation.custhelp.com/app/answers/detail/a_id/19719/page/1

Mickey · Jul 30, 2018

See pdf for data format (yes it's free)

1762-IF4 Questions

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