Troubleshooting

Hi,
I have AB-micrologix 1200 plc.
I connect my sensor with Sensor monitor.Monitor measure sensitivity
in %. that monitor have 4-20 ma analog output.that output connect
with my plc analog input.so plc show same reading as Monitor.
but plc does'nt show exact reading.
when I told to my programmer he said me there is problem with monitor.
and then I talked with monitor manufacture they told me problem with
programming.

i want to know how i can trace where is problem?

Thanks,

pratik

Get a digital volt meter that can read 4-20 mA signals, and put it in the loop(s). See which device matches the 4-20 mA signal.

What is the "monitor" reading? Is it same signal,
or signal received from PLC? What is the difference
in readings? What is the accuracy you are expecting?

Hi,
my monitor measure 48% and my 4-20mA output measure 11.7mA.

and my plc measure 94%.my programmer use SCP instructon.

Thanks,

pratik patel

What the max measurement of your sensor?

the max of the sensor is 20mA.
Take the all range of the sensor (-X)to(+Y)=Z

16/Z will give you how much unit in mA

Now Check if 11.7 mA is make sense.

another option tell your programer to check his scaling in the program.

Or send me all the details I will do the calculation.

Are you using the 1762-IF4 analog input module ? It has two different input scaling options; Raw Data or "Scaled for PID". You can change these in the Output data table of the module. Have a look at the 1762-IF4 user manual for details on setting the data format.

http://www.ab.com/manuals/cp/1762-in012a-en-p.pdf

The User Manual doesn't include an explicit list of the numeric data ranges that correspond to various real input ranges. That information is fortunately included in a Knowledgebase document, number G19893.

If the 4-20 mA output of your sensor represents 0 - 100% of a condition, and you want 0 - 100 as the data values in your MicroLogix 1200, then your SCP instruction should be set up like this :

[attachment]

The Input min/max values come from the 4 and 20 mA values in the Knowledgebase document.

my monitor measure 48% and my 4-20mA output measure 11.7mA.

and my plc measure 94%.my programmer use SCP instructon.



If... that's "IF"...

4 mA = 0% and 20 mA = 100% then...

    +------------ (B) ---------+

    |                          |

    +---- (A) ----+            |

    |             |            |

   4 mA        11.7 mA       20 mA



    0%           X%           100%

    |             |            |

    +---- (C) ----+            |

    |                          |

    +------------ (D) ---------+

The ratio of A to B is equal to the ratio of C to D...

That is... A/B = C/D...

That is, The ratio of (11.7 - 4) to (20 - 4) is equal to...
the ratio of (X - 0) to (100 - 0)

           7.7       X

           ---  =  ----- 

            16      100

Solving for "X",

X = ( 7.7 * 100 ) / 16 = 48.125%

Better have a talk with that programmer.