Hardwire monitoring

The ARC is controlled by its own hardwired control module. The temperature is monitored by a set of seven thermocouples connected in series which measure the difference between the temperature of the sample and that of its surroundings. The temperature is maintained by heaters which receive their inputs from the control module. A pressure transducer is attached to the sample container, giving both an analog readout on a pressure gauge and a digital readout on the control module panel. It should be noted that pressure is monitored but it is not part of the control loop. 

Most of the system interlocks are handled by the embedded NI controller. This is similar to that used in other laboratory-scale reactor systems (Mills and Nicole, 2005) except the Siemens 545 PLCs have been replaced with the National Instruments system. The National Instruments controller monitors the status of the AIMS process variables and takes appropriate action if any interlock conditions are found. In addition to these interlocks, the external heater controllers that are used for the system heating tapes and sampling valve box contain hardwired overtemperature interlocks built-in to these controllers. However, these interlocks only interrupt power to the affected heating device, so the NI controller must still take action to shutdown the rest of the process. 

It has been possible to interface such systems to the main production OCS for awhile, but this has been achieved via de facto standards that have made it difficult or even impossible to exchange additional information beyond the basic controlled parameters. For example, although the humidity and temperature of the production area ambient air could be measured and recorded within the OCS (via serial interface or hardwired transmitters, for instance), it has not been possible to monitor the load, temperature or efficiency of the main air-conditioning unit fans. 

Completely independent safety monitors to prevent common flaws. This includes signal sources, different component models and different program types Hardwired safety circuit and critical devices such as track limits and slack rope Strict software revision control... 

Hardwired alarm for safety. DCS, distributed control system ESD, emergency shutdown LVM, limit value monitor PLC, programmable logic controller PS, power supply. 

One should appreciate that in any system there will be a short period during transitions when outputs may not be wholly consistent. As mentioned earlier, the duration of these inconsistencies should be short compared with associated plant dynamics, this includes any hardwired protection systems which monitor PES outputs. 

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