1762-of4

[kurt.brinker]

Micrologix 1100 unit with an 1762-OF4 analog output card. The card is configured for a 4-20mA / scaled for pid. It gets a scaled value of 0-16383 in the program to determine its output. The problem is that it the output is 0-21mA instead of 4-20mA. In the manual it says that normal range is 4-20 and full range is 0-21. The manual says, "The over- or under-range flag comes on when the normal operating range (over/under) is exceeded. The module continues to convert the analog output up to the maximum full scale range."


What causes the module to enter this condition? Any ideas on our problem?

 

[curlyandshemp]

Micrologix 1100 unit with an 1762-OF4 analog output card. The card is configured for a 4-20mA / scaled for pid. It gets a scaled value of 0-16383 in the program to determine its output. The problem is that it the output is 0-21mA instead of 4-20mA. In the manual it says that normal range is 4-20 and full range is 0-21. The manual says, "The over- or under-range flag comes on when the normal operating range (over/under) is exceeded. The module continues to convert the analog output up to the maximum full scale range."


What causes the module to enter this condition? Any ideas on our problem?

Scale the analog output using the SCP instruction,so that 0 counts = 4ma and 16383 = 20ma

 

[kurt.brinker]

thats how it is now. with the value at 0 it gives us 0 ma out and with the value at 16383 it gives us 20.9mA out.

 

[SNK]

The OR and UR are used for detection of OPEN cct or SHORTED CCT.
You can use the flags in your program for diagnosis of faults.
As Curly&Shemp stated, you need to scale the output to your Transmitter in your program.

 

[curlyandshemp]

thats how it is now. with the value at 0 it gives us 0 ma out and with the value at 16383 it gives us 20.9mA out.

On your SCP to the analog output channel
try
Scaled Min = 3120
Scaled max = 15600

That should get you close to 4-20ma output

 

[kurt.brinker]

the output to the transmitter IS scaled. We have an analog input that is scaled 0-16383 and that number is transfered directly to the output channel. We get 4-20mA in from the flowmeter and we want to send the exact same mA out so the customer knows the current flowrate.

Are you saying i need to modify my output scale from 0-16383 to 3277-xxxxx and just tweak the numbers until my output is correct?

 

[kurt.brinker]

On your SCP to the analog output channel
try
Scaled Min = 3120
Scaled max = 15600

That should get you close to 4-20ma output

ok, thats what i was doing in the field and it just struck me as odd that i needed to adjust the scales so drastically. thats what i'll do tho. thanks

 

[nettogrisen]

This is because you don't want 0-20 mA, you want 4-20.
0 = 0 mA
3120 = 4 mA
15600 = 20 mA