MicroLogix 1200 Series C

[tbansal]

Hi everyone,
I have been trying to work on an issue in AB MicroLogix Series C with an analog module IF4 for quite some time now, but now am reaching a frustration level.

What I have is a Omega Pressure Transducer on a circuit board. This transducer has three valuable pins. Pin 1 gets the Voltage, Pin 2 is grounded, and Pin3 provides the Output.

Now I have connected this Pin3 to the In0(+) of the analog while the In0(-) is grounded. If I take a voltmeter and read the voltage across, I do get a 0.5 V across the PLC contacts and circuit board, which is correct.

Additionally, I have properly configured the 'IO Configuration' in RS Logix 500 5.5. (Filter: 60 Hz, 450 ms, Input Range: -10 to 10VDC, Data Format:Raw/Proportional)

When I go online, I read the Data File Input Register I:1.0 but to no avail. It gives me a Radix Decimal value of approx 1534. The value does change if i provide some pressure to the Transducer.

My problem is that I can't relate this value of 1534 to anything. It doesn't appear to be a voltage or a current reading. Does anyone know how to appropriately interpret this value????

Any help would be greatly appreciated...
Thanks in advance !!
tushar

 

[Ken Roach]

The 1762-IF4 is a 15-bit resolution module, and you have it in Raw Data mode.

The traditional range for a fifteen-bit value (with a sign bit) is -32768 to +32767 (decimal). Those are the values that will correspond to -10 V to +10 V input on this module.

There's a little variance there; this module will measure up to 10.5 volts, so +32767 = 10.5 V, and +31206 = 10.00 V. (I got this info gem from Knowbase document G19893 on the support.rockwellautomation.com site)

Your reading is 1534, so do a little math and (1534 /31206) * 10.0 = 0.4915 volts.

You have to scale the raw input data in your ladder logic, so that the unscaled input value corresponds to the desired number of volts, or psi, or ft/min, or turtles/tureen. The SCP instruction is ideal for this purpose.

 

[Ron Beaufort]

maybe this will help ....

Take a look at page 4-11 (Adobe page 49 of 88) in this manual for the 1769-IF4:

1769-IF4 user manual

This chart shows the data values which result for different scaling selections. If you’ve set it up the way your post indicates:

then -10V would give -31206 ..... and +10V would give +31206 .... so 1560 would be the “dead on” data reading for +0.5V .... your reported 1534 is pretty durn close.

Tip: Unless you really need those negative readings, then you might consider using the 0.0V to +10V scaling selection.

If you need more help than this, it would be a good idea to tell us the scaling of your pressure transducer. Then we could really get serious about how to convert and interpret the data reading into any units that you require.

PS edit: Ken beat me to the punch - but I'll leave my post here since it includes the link to the user manual.

PPS edit: "turtles/tureen" ...? never heard that one before ...

 

[tbansal]

Thanks a lot Ken !! That makes a lot of sense. I will try that.

 

[tbansal]

Thanks Ron. Here is a link to the Pressure transducer that I am using.

http://www.omega.com/Pressure/pdf/PX40.pdf