General Discussion

The following link describes some significant disasters thaI have been caused by process control failure.

https://controls.engin.umich.edu/wiki/index.php/Failures_in_Process_Control

Process control modules are accustomed to both sense particular states (such as temperatures, pressures etc.) and to control or regulate process components in the system that change things like flow rates (valves), heating input signals (burners, boilers etc). and other parameters that effect the functioning of the method and determine the quality (and safety) of the output from the process.

From electronic signals and sensor modules sent to control modules are similarly significant, digital signals obtained from a security standpoint. Even if all the sensor and control modules will work correctly, if the electronic signals electronic send or receive are too feeble to be interpreted correctly, the consequence may be a process control failure. The effects of a process-control failure is often as sensational as the Bohpal, three-mile Island or Texas City Disasters.

The pathway that carries these electronic indicators is called a network. If, for whatever reason, the part of the community itself are deficient such the signals are too poor to be interpreted properly, management instructions and both sensor info could be negatively influenced. Electronic signal quality can decrease as the physical amount of the network boosts or because of interference (commonly called “sound”) from resources external to the community itself. Network requirements that explain how a network should be anticipated to function will normally quote an optimum physical length and certainly will notice any characteristics of the community that are accustomed to counter “noise” in the system and / or to maintain signal quality over this optimum physical span.

When writing these network specifications, the network manufacturer’s engineers make suppositions in regards to the minimum strength of the digital signals that are sent by sensor modules along with the minimal strength of the digital indicators which can be received and interpreted correctly by control modules.

In the case of the Allan Bradley (AB) Data Highway Plus (DH ) network, AB’s community engineers suppose that all the detector and control modules will be types which are made by A-B and, hence, the minimum signal strengths sent and received by these AB modules are well recognized and may be assumed when composing the network requirements.

If, however, several of the detector or control modules that are on the AB DH network don’t reliably send or receive the presumed minimum strength electronic signals, the community might not be able to work properly over its given maximum length that is physical. Moreover, in the event the electronic signal strengths of these sensor or control modules are weaker in relation to the presumed minimums, the noise-countering features of the network might be unable to maintain the essential (and safe) signal quality.

Electronic signal strength is measured in models of “peak to peak voltage (Vpp)”* at the “port” (bodily connector through which electronic signals enter or leave a process control module) of a process control module under different load (resistance measured in Ohms) conditions.

The evaluations previously described demonstrate the peak to peak voltage (Vpp) measured for the Datalink GW1000 modules produced by Datalink are considerably below those quantified for Equustek modules or equivalent AB.

The danger raises that the Data highway Plus community may not perform as stipulated. That is, it may not be safe to attempt to operate the DH community at its stated maximum length that is physical. These lower Vpp voltages also increase the chance that any sound-countering attributes of the A-B DH community might not perform as specified. This may additionally contribute to conditions that are dangerous for people who may be exposed to a process handle failure.

Most of the failures would not be dramatic. Many of them would go unnoticed, or the resulting action would probably be blamed on something other than the network. No trace of the error will remain after it occurs, other than the resultant damage.