Replacing a PLC with LabView Article

[Jack-Lane]

I just read the article "Replacing a Programmable Logic Controller (PLC) with LabVIEW and FieldPoint for Composting Plant Automation ". I am very concerned by the author's lack of knowledge about current PLC's. This article does not fairly compare the two platforms and is not accurate. For example, the author states that 100 msec is a typical response time for a PLC. This is absurd. Today, even low end PLCs can achieve responses time below 10 msec and high end PLCs even as low as 1 msec. It all boils down to specifying the right hardware for the application. One real danger the author does not address with building a "soft PLC" is the potential for the I/O not to fail to a safe condition if the operating system (Windows) lock
s up. This can be disastrous and unsafe for many control applications. I would suggest any reader that is seriously considering replacing a PLC in an industrial environment with a "soft PLC" watch out for this potential shortcoming. Readers can visit www.isa.org to find additional information on this issue.

I would not dispute that for a pure data acquisition application LabView can offer a superior solution. The safety conern can be mitigated if there is a "hard wired" safety system that has been properly designed. However, many times the PLC may provide safety shutdowns that depend on its true deterministic operating system and high reliability.

I hope that readers will not interpret this as a slam against LabView but as encouragement research this issue further from a different perspective.

[Process_Systems]

I can see from your comments that you have a firm grasp of the PLC/vs PC concept, and agree with your comments. I have been an instrumentation developer/integrator for 36+ years, and have first hand experience with the situation(s) to which you refer. I have found the optimum solution has been a combination of PC/MMI software and PLC hardware. I have many such systems up and running in different industries, and have found this to be the best overall solution. Let the PC do what it does best(MMI display, complex calculations and decision making), and the PLC what it does best(solid deterministic control, with a non-windows operating system). I usually use an OPC server for communication between the two units, and with proper software design on both ends,
and a hardwired E-Stop system, excellent overall opertion/safety is achieved.

Your comments should serve as good stimulus for other developers.

Dave

[swappy]

Sir,

Does it mean for fail safe action we cant use labview and its better to use a PLC instead ? i have a project which is running on plc and i want to replace the costly PLC with many inputs and outputs by labview .will daq be a good approach to it? or still plc is a better option?