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LDmicro Forum - PLC and safety

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PLC and safety (by Zdenek Hajek)
Dear Sir,

I would like to say thank you. I personally consider LDmicro the most exciting action in the world of LD programming for AVR and free software.

However, I have to warn you about a security issue. LDmicro generates a code that is not safe for PLC applications.

Standard PLC operates in continuous loops. It reads the values of all physical inputs before entering the loop and writes them to the Input image. The system creates an Output image for the physical outputs. Then it operates with these values during run time. After that, rewrites the values from the Output image to the physical outputs at the end of the loop. Industrial devices are moving, the status of the buttons, sensors, motors and various types of motion is constantly changing. It is not acceptable and safe to have different states of physical input at various points of the program and give inconsistent results during one program cycle. It is not possible that in one rung motor (or engine) is physically powered on and in second rung is turned off and somewhere else again turned on only because output variable is several times changed during one program cycle. In short… Last valid states of output variables are rewritten from an output image to real physical outputs. That is a problem in the case of LDmicro as well.

I propose two resolutions:
• Create system tables of copies of values and do initial scan of input state and after program cycle make final output record by system itself (write output variables to corresponding registers/pins).
• Inform LDmicro users about this fact. Recommend them to transfer the state of the repeatedly used contacts (prefix X) and coils (prefix Y) to local variables of type Internal Relay (prefix R) X, Y → R and work exclusively with them. Finally, they must rewrite the values R → Y at the end of the program.

Yours sincerely,

Zdenek Hajek
Sat Mar 3 2018, 17:36:21
(no subject) (by Magno Medeiros (Brasil))
Hi, Zdenek Hajek.

with all respect to your arguments I just want to record that I use clp, s coontruidos by myself and using LDmicro more than 5 years, and until today I had no problem related to this. only defects such as scratches that ruin contacts or burning of voltage regulator for example. Anyway I agree with you that we should take security measures yes!

Magno Medeiros.
Sat Mar 3 2018, 19:47:09
(no subject) (by MGP)
Everyone is responsible for his products.

Few can afford a safety certificate and therefore you should not worry too much about the programming method of LDmicro.

I do not know any programming language that meets the safety requirements and if it is really necessary you have to buy an industrial PLC such as AB, Siemens etc ...
Sun Mar 4 2018, 09:13:21
thank you (by oleksiy)
Hi Zdenek.

Thank you for your suggestion.
Mon Mar 5 2018, 08:32:49
por Zdenek Hajek (by Calubert)
Los sistemas de seguridad Para PLC los hace el Programador las salidas que se usen de potencia solo las debe activar reles internos.
Ejemplo:

LD X1 R100 aquí se hace el programa de todas las variables.
esto dirá que cuando el plc tenga alimentación lea todo pero no hará nada hasta que se le de la orden de operación (un Ciclo).

Parece ser que seles quiera dar miedo a la gente no te guardes nada que cuando uno falta la vida sigue.....
Tue Mar 13 2018, 08:27:34
PLC and safety (by Ihor Nehrutsa)
Tue Apr 24 2018, 09:40:29
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