So, we have one servovalve that is very critical to machine operation and idea is (or was) to detect if valve gets disconnected from analog output card. I enabled all diagnostics on analog output card, but when valve is disconnected (wire break) there is nothing coming from diagnostics, so we can't detect servovalve fault. Card is question is AQ 4xU/I ST (6ES7 135-6HD00-0BA1I Is there something I'm missing out? Is it possible to do what I'm trying or?
Detecting analog output fault in Siemens S7-1500
- Thread starter doomsword
- Start date
cardosocea
Member
Does the card report a fault on the LEDs?
I_Automation
Lifetime Supporting Member
For analog outputs that are critical I wire the output to an analog input and monitor it.
For a voltage output just add a second cable off the output & wire it to a voltage input.
For a mA output loop the output through the mA input. This will also detect a signal loss due to a wire break, as where the voltage wiring above will only detect the output failing.
EDIT: Also it is common to add feedback from the process as far down the line as can be. VFD at running speed; motion detector at the far end of a conveyor; pressure, flow or vacuum sensor after a pump; whatever else is appropriate to monitor the output.
For a voltage output just add a second cable off the output & wire it to a voltage input.
For a mA output loop the output through the mA input. This will also detect a signal loss due to a wire break, as where the voltage wiring above will only detect the output failing.
EDIT: Also it is common to add feedback from the process as far down the line as can be. VFD at running speed; motion detector at the far end of a conveyor; pressure, flow or vacuum sensor after a pump; whatever else is appropriate to monitor the output.
Last edited:
You should be getting at least a red light on the IO card, a red light on the PLC (or maybe orange), a message in the diagnostic buffer, and a system diagnostics alarm.
1) it could be worth recompiling HW and SW and downloading HW and SW, just to make sure you didn't miss something.
2) When you go online with Portal, does it show errors? Does it show an alarm in the Alarm display?
If so, also check to make sure that all your alarm classes are available on the alarm view on the HMI, by default it doesn't include the PLC alarms.
1) it could be worth recompiling HW and SW and downloading HW and SW, just to make sure you didn't miss something.
2) When you go online with Portal, does it show errors? Does it show an alarm in the Alarm display?
If so, also check to make sure that all your alarm classes are available on the alarm view on the HMI, by default it doesn't include the PLC alarms.
No, I don't see anything, everything looks fine.
Servovalve is +-10 mA, card is +-20 mA, so I just scale it to match the ranges. Could reason for not seeing any fault be that output is bipolar?
I do have servovalve spool feedback (4-20mA), which would tell me if something is wrong with the valve (valve reference being sent but valve doesn't respond ), but reaction to this servovalve control fault should be practically immediately. Also spool feedback might have wire break but servovalve itself might be fine and I would stop it for no real reason.
Regarding wiring it that might be done if there is no other way to do it.
Hardware configuration was 100% downloaded, I am sure all diagnostics settings are enabled. No any fault seen when I'm online with TIA Portal. This is what confuses me
Please list the exact type numbers of all the PLC devices.
In S7-1500, some diagnostics is only available in 'high feature' versions of the IO modules and/or the IM modules.
'wire break' monitoring is possibly only supported with 4-20mA signals.
In S7-1500, some diagnostics is only available in 'high feature' versions of the IO modules and/or the IM modules.
'wire break' monitoring is possibly only supported with 4-20mA signals.
This could be the way to do it.I_Automation said:
I_Automation
Lifetime Supporting Member
Yes to this, but if the output is considered "Critical" in my application I still loop the output through an input to make sure the signal is getting out.
With a spool feedback I would monitor that, and also have a process device I monitor (pressure, flow, velocity, temperature, etc.) along with discreet sensors (minn pressure, max pressure, limit switches, motion detector, level switches, etc.)
PLC: S7-1500 v2.8
IM module: IM 155-6 PN/2 HF (6ES7 155-6AU01-0CN0) v 4.2
card: AQ 2xU/I HS (6ES7 135-6HB00-0DA1) v2.0
So, signal is +- 10 mA (card is +-20 mA), is this bipolarity that is causing to be unable to detect a fault? Because I vaguely remember this working with some analog outputs some years ago?
I managed to get this thing working. It didn't work at beginning since it was connected to ST rack, which doesn't support advanced diagnostics.
We reconnected to HF rack since we needed very fast control and once I enabled diagnostics it is possible to see a channel fault.
Now, I detect channel faults by RARLM function inside OB82 (I/O FLT interrupt OB) where I can see which channel faulted and set corresponding analog output bit.
Now where I have an issue is following situation:
-I correctly detect which channel faulted and can see when both channels (we have two servovalves) are faulted
-then one channel gets reconnected but I can't tell which channel got reconnected (if both get reconnected then is easy, I just check card status with GET_DIAG and clear the faults
So, is there reverse function of RARLM, that gets activated once I/O fault is cleared?
We reconnected to HF rack since we needed very fast control and once I enabled diagnostics it is possible to see a channel fault.
Now, I detect channel faults by RARLM function inside OB82 (I/O FLT interrupt OB) where I can see which channel faulted and set corresponding analog output bit.
Now where I have an issue is following situation:
-I correctly detect which channel faulted and can see when both channels (we have two servovalves) are faulted
-then one channel gets reconnected but I can't tell which channel got reconnected (if both get reconnected then is easy, I just check card status with GET_DIAG and clear the faults
So, is there reverse function of RARLM, that gets activated once I/O fault is cleared?
I managed to get this thing working. It didn't work at beginning since it was connected to ST rack, which doesn't support advanced diagnostics.
We reconnected to HF rack since we needed very fast control and once I enabled diagnostics it is possible to see a channel fault.
Now, I detect channel faults by RARLM function inside OB82 (I/O FLT interrupt OB) where I can see which channel faulted and set corresponding analog output bit.
Now where I have an issue is following situation:
-I correctly detect which channel faulted and can see when both channels (we have two servovalves) are faulted
-then one channel gets reconnected but I can't tell which channel got reconnected (if both get reconnected then is easy, I just check card status with GET_DIAG and clear the faults
So, is there reverse function of RARLM, that gets activated once I/O fault is cleared?
My understanding is that OB82 gets called both when the error happens, and when the error is resolved. RALRM should provide in the AINFO whether or not the alarm is INCOMING, meaning that it just happened, or OUTGOING meaning that it is now resolved. In the ChannelDiagnostics detail section of the data, it's in byte 4, bits 3&4.
Personally, I think RALRM is dumbly complicated, and feels like a holdover from the 300s and doesn't feel very 1500/symbolic/etc. It's the only way I know of to get SPECIFIC error codes tho (wire break, short circuit, etc). The system creates the alarm text for me for the operator to deal with, my logic only cares if it's good or bad, not the details of how it's bad. There's a checkbox in your IO card to activate Value Status, which adds an extra IO area that returns for each channel a 1 if it's OK and a 0 if it's bad for any reason (no power, wire break, etc). That's what I use instead of messing with RALRM.
I just came to write I figured it out (this thing with incoming and outgoing OB82 calls) while checking how RALRM function works.
I also checked this about value status and I really think this is the way it should be done, so when I have opportunity to stop the system I want to check this.
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