Siemens Analog input card - PLCS.net

rajendrad · May 2nd, 2003, 05:23 AM

IN THE RECENT COMMISSIONING I HAD FACED SIEMENS MAKE ANALOG OUTPUT CARD FAILURES.WHILE CHECKING THE SYSTEM I NOTICED THAT 24VDC INPUT TO THE CARD IS VARYING FROM 19VDC-25VDC.THIS IS BECAUSE SOLENOID LOAD IS ALSO ON THE SAME POWER SUPPLY.IS SUCH POWER SUPPLY WILL CAUSE FAILUARE OF ANALOG OUTPUT CARDS ???????????

RRobbins · May 2nd, 2003, 09:14 PM

Please, turn off the capitals. WE CAN HEAR YOU!!

Now, you were using a digital meter, I'm guessing. The voltage was dropping lower, but you meter averages for short times and misses the peaks, up and down. The cards are not designed to have fluctuating power and puts a huge load on the solid state componets. The filters can't filter out everything and I guess a spike wiped you out. Seperate the power supplies.

icky812 · May 5th, 2003, 08:56 AM

What RRobins said is certainly accurate. A lot of times what happens is that the DC solenoids do not have surge suppression on them. So when they are turned off the reverse voltage spike travels back up the line and starts destroying the weakest device on the line. In this case the Analog Output cards.

Transorb diodes or MOV's placed across the coil are very cheap insurance against this type of failure. DC coils are the worst, but AC coils should have surge suppression as well. I talk with people everyday that have destroyed a high dollar plc, touchscreen, or other piece of equipment from not using surge suppression.

Fritz_frederix · May 5th, 2003, 09:41 AM

Rajendrad,

A litlle while ago I also had kind of the same problem, what RRobin
is saying is certainly true but it also can be another thing.
Earthing, make sure that the earth of your plc is properly
connected. Also be sure that one site of the powersupply is
earthed. It's a typical Siemens problem.

Best regards Rudi

May 2nd, 2003, 05:23 AM	#1
rajendrad Member Join Date: May 2003 Location: Pune, India Posts: 19	Siemens Analog input card IN THE RECENT COMMISSIONING I HAD FACED SIEMENS MAKE ANALOG OUTPUT CARD FAILURES.WHILE CHECKING THE SYSTEM I NOTICED THAT 24VDC INPUT TO THE CARD IS VARYING FROM 19VDC-25VDC.THIS IS BECAUSE SOLENOID LOAD IS ALSO ON THE SAME POWER SUPPLY.IS SUCH POWER SUPPLY WILL CAUSE FAILUARE OF ANALOG OUTPUT CARDS ???????????

May 5th, 2003, 09:41 AM	#4
Fritz_frederix Member Join Date: Apr 2003 Location: Belgium Posts: 433	Rajendrad, A litlle while ago I also had kind of the same problem, what RRobin is saying is certainly true but it also can be another thing. Earthing, make sure that the earth of your plc is properly connected. Also be sure that one site of the powersupply is earthed. It's a typical Siemens problem. Best regards Rudi __________________ We're going to save money, no matter what is costs

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May 2nd, 2003, 09:14 PM	#2
RRobbins Lifetime Supporting Member Join Date: Dec 2002 Location: Richmond, VA Posts: 400	Please, turn off the capitals. WE CAN HEAR YOU!! Now, you were using a digital meter, I'm guessing. The voltage was dropping lower, but you meter averages for short times and misses the peaks, up and down. The cards are not designed to have fluctuating power and puts a huge load on the solid state componets. The filters can't filter out everything and I guess a spike wiped you out. Seperate the power supplies.

May 5th, 2003, 08:56 AM	#3
icky812 Member Join Date: May 2002 Location: Cumming, GA Posts: 579	What RRobins said is certainly accurate. A lot of times what happens is that the DC solenoids do not have surge suppression on them. So when they are turned off the reverse voltage spike travels back up the line and starts destroying the weakest device on the line. In this case the Analog Output cards. Transorb diodes or MOV's placed across the coil are very cheap insurance against this type of failure. DC coils are the worst, but AC coils should have surge suppression as well. I talk with people everyday that have destroyed a high dollar plc, touchscreen, or other piece of equipment from not using surge suppression.

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