1734-IB8 holds it's previous state on power failure

aparnac · Apr 19, 2010

We are using Controllogix CPU L43 & Ethernet Module 1768-ENBT on 1 bus & 6 Remote IO station.In RIo we are using 1734-AENT communication module & Point I/O's.

In RIO side we are facing a problem, when RIO power fails, 1734-IB8(Digital I/P) Module holds it's previous state.

I was increased RPI rate but it won't work. is their any other way to solve this problem?

rdrast · Apr 19, 2010

1) Keep the RIO power from failing? Feed it from the main PLC source, battery backup, UPS?

2) Don't use the IO point tags directly, copy them to an internal array of bools, and use those through the program. Query the state of the module(s), with GSV instructions, and if you see a fault, zero out the set of bools.

Look up the GSV instruction, particularly the class "MODULE", and attribute "EntryStatus". Mask off the upper four bits (MVM ModEntryStatus 16#F000 ModEntryStatusMasked), and compare with 16#4000 (EQU ModEntryStatusMasked 16#4000). If that is true, the module is running, if false, the module is not in a normal run mode.

aparnac · Apr 19, 2010

rdrast said:
1) Keep the RIO power from failing? Feed it from the main PLC source, battery backup, UPS?

2) Don't use the IO point tags directly, copy them to an internal array of bools, and use those through the program. Query the state of the module(s), with GSV instructions, and if you see a fault, zero out the set of bools.

Look up the GSV instruction, particularly the class "MODULE", and attribute "EntryStatus". Mask off the upper four bits (MVM ModEntryStatus 16#F000 ModEntryStatusMasked), and compare with 16#4000 (EQU ModEntryStatusMasked 16#4000). If that is true, the module is running, if false, the module is not in a normal run mode.

Thanks for your help.
We want to know this problem can be solved by upgrading CPU firmware? or EDS file?

rdrast · Apr 19, 2010

As far as I know, no. Over ethernet, there isn't any automatic means of setting the input state in the event of loss of comms.

Write the program properly to deal with it, or don't. Unfortunately, that is up to you.

Even in cases where there ARE automated 'safe-state' values under certain circumstances, if you must rely of the safe-state being applied, you should get in the habit of double and triple checking yourself. Monitoring the module status entry is about the best way I can think of.

Ken Roach · Apr 19, 2010

rdrast is exactly correct.

"Going to zero" is a bad way of detecting a module failure if "being at zero" is a legitimate and correct value for the input device.

Your input module works exactly the way it is designed to work.

I always write logic with GSV instructions to check the Connection status of remote devices so that my logic can take action if they are disconnected from the network.

If you are using a "Rack Optimized" connection to handle the discrete I/O, you can also check the Module Status word that comes with the Input connection; if all 32 of the Module Status bits are = 1 (total value of DWORD = -1) then the connection is broken.

aparnac · Apr 20, 2010

Thanks Rdrast & Ken Roch. Problem is solved.......

naag_slet · Apr 21, 2010

L32E CPU holds it's previous INPUT DATA on 1734-AENT, IB8 OR OB Failure

Hi to All,
Actually today i had tried with this concept,but no result..
i have L32E cpu and 1734AENT with IB8 and OB8(in the testing kit)
please have a look into the attached RSLOGIX5000 file and have a look the programme in the main routine if wrong please suggest the right programme..
My requirement is when IB8 OR OB8 OR 1734AENT fails input status has to set back to '0'.INSTEAD OF SHOWING LAST STATE.

Many Thanks in advance..
Naag.

rdrast · Apr 21, 2010

Do a GSV to get the MODULE status then for each module. If any fail, zero your (internal) I/O.

This is a basic rung to tell if a module is running or not. Note: the "Instance Name" field is the actual name of the module as defined in the I/O tree.

BST GSV MODULE E2_TC1 EntryStatus MOD_E2_TC1_Status AND MOD_E2_TC1_Status 61440 MOD_E2_TC1_Status NXB XIC MOD_E2_TC1_Status.14 OTE MOD_E2_TC1_Running BND

naag_slet · Apr 21, 2010

Many thanks to Mr.rdrast,
i will try this concept and get ack to you wih results,
Naag.

naag_slet · Apr 22, 2010

ya its working fine...
Thanks to all..

May i know how to do same thing in the SLC family?Monitoring SLC local rack (each module)status and remote i-o status.
Also I want to set zero for all the input data when the slc cpu goes to faulty..how to do
Mnay thanks in advance,
Naag.

rdrast · Apr 22, 2010

The SLC will hard fault out on an I/O problem for local (and local extended rack) faults, making the state of the inputs irrelevant.

For Remote I/O, depending on the network, there are status bits available for each remote rack, but I can't go into more detail on that.

naag_slet · Apr 22, 2010

can you give some hint on regard?
Naag.

naag_slet · May 4, 2010

Hi guys,
Actually i observed a problem in the 1734 IB-8 with obove concept.if module faulty or loose contact it is triggering the Faulty bit and this bit is animating in the SCADA that repective module is faulty..

Observed problem is if one or more than one channel got faulty(out of 8 input channel in the IB-8)Below logic won't working.

BST GSV MODULE E2_TC1 EntryStatus MOD_E2_TC1_Status AND MOD_E2_TC1_Status 61440 MOD_E2_TC1_Status NXB XIC MOD_E2_TC1_Status.14 OTE MOD_E2_TC1_Running BND

So is any other way to daignosie the indidual channels status?
Thanks in advance
Naag.

1734-IB8 holds it's previous state on power failure

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