Monitoring of stirring speed
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How should the mixing speed fed into the SIS interlock be monitored? Can a current transducer be used in the MCC to monitor the current? Won’t this be inaccurate?
You can consider using digital signals for monitoring; the digital output points from the speed high/low sensors can be fed into the SIS system
It is generally current monitoring to save costs
For the SIS system, the reliability level should be SIL1 or higher. It’s not easy to determine the relationship between current monitoring and rotational speed; I thought it would be convenient to use a proximity switch with SIL certification, followed by a counting module from PCS that also has SIL certification, so that the rotational speed can be measured within the SIS system and compared with the set values. Alternatively, a counting module with switches could be used to set upper and lower limits, with signals sent to the SIS system in case these limits are exceeded. A metal block is welded to the main shaft; when the proximity switch makes contact, a pulse is generated, which corresponds to one rotation, and the counting module can use this to determine the speed
As long as there is an exposed part of the stirring shaft, it can be monitored; a speed sensor and an acceleration safety barrier are used, and then the actual rotation speed can be measured by the DCS system.
Wouldn’t it be better to directly obtain the frequency conversion signal from the inverter of the mixing motor and use it after conversion?
6th floor; it may be necessary to take the slip rate into consideration. On-site measurement is more accurate. If requirements are not high and the load is not large, it’s convenient to obtain signals using frequency conversion.