I am using a panelview plus 7 HMI which displays temperature readings in an analog indicator, however after sometime the analog values show random readings which go out of scale. i have checked scalings and everything is proper, when PLC and HMI is powered on, everything works fine but after an hour or so the HMI starts showing random value.
Analog display on HMI
- Thread starter RJ29
- Start date
Jasondelane
Lifetime Supporting Member
If you view the data in RSLogix, are you getting the same bad readings?
NO, the analog values are proper, its just the HMI that is creating problems, had it been an issue since the beginning , i would have figured it out, but the analog readings start showing full scale readings in between.
the actual analog input is 16 ma and i get the corresponding 70 degree reading initially, but after some time,the actual analog input is still 16 ma and i get 108 degree which is not even in my range
the actual analog input is 16 ma and i get the corresponding 70 degree reading initially, but after some time,the actual analog input is still 16 ma and i get 108 degree which is not even in my range
busarider29
Lifetime Supporting Member
Was there some work done on the machine since the problem started? Is there somewhere else in code that maybe is getting written to that PLC variable?
janner_10
Lifetime Supporting Member
Make a temporary new numeric display alongside the suspect one and point it to the scaled analogue value in the PLC.
Compare the two when the first is reading incorrectly.
Compare the two when the first is reading incorrectly.
Nope, this problem started recently, i took the system online and found that the analogue readings are proper i get a count of 12100 properly when i monitor the analog pin and as per my scaling calculation it converts properly to 70 degrees, even the tag is linked properly to HMI numeric display..
Tried it already, both the displays show same readings
Logically since both of them are linked to same scaled tag
That could be an issue since my system is operating near a very high current Rectifier ( 30kA) , will check the same for inteference and as a precaution I'll use shielded wires for analogue inputs and outputs.. Let's see what happens.. will get back to you soon
If it was interference the you should see it in the PLC too. You can write a trap in the PLC so if the value goes high you latch a bit or move the value into a holding register. Then you will know for sure if its happening in the PLC
Vlad Romanov
Member
As others mentioned, I'd start with troubleshooting the PLC signal first. It's highly unlikely that a simple HMI read would cause the value to fluctuate or change from what it is on the PLC.
Write a very basic trap that would do the following:
IF (current GRT saved) MOVE (current to saved)
I'm assuming that pseudocode is fine and I don't need to show the ladder implementation...
That way you can capture the highest reading and you can rule out that this isn't happening on the PLC
My initial guess is that it's either interference, problem with the wiring or a setting on the sensor.
Cheers,
Vlad
Write a very basic trap that would do the following:
IF (current GRT saved) MOVE (current to saved)
I'm assuming that pseudocode is fine and I don't need to show the ladder implementation...
That way you can capture the highest reading and you can rule out that this isn't happening on the PLC
My initial guess is that it's either interference, problem with the wiring or a setting on the sensor.
Cheers,
Vlad
Should have done that in the first instance.
Also make sure your cable shields are only grounded at one end only. Grounding both ends could create a Ground Loop, i.e. passing current, in the cable shields
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