PLC versus DCS
PLCs and DCS play a major role in Industry Automation controlling Modern manufacturing Plants and Factories. Over the years due to continuous development and functionality merging between PLCs and DCS. The border Line of Differences became obscure. This blog post will lay out the differences between the both to facilitate automation Engineer in choosing the best Systems ( PLC or DCS) for their Project.
Below are just my personal Opinion and Comparison , it does not Represent any Company
PLC versus DCS Selection
| NO | Subject Comparison | PLC | DCS |
| 1 | Speed | 20ms to 100ms | 80ms to 800ms |
| 2 | Down Time Recovery | Depend on Controller Architecture | Design to Switch Interoperability |
| 3 | Process Batch Control | Can do Batch Control but Specialize in High Speed Process | Specialize in Batch Control |
| 4 | Flexibility | Design For High Program Modification | Rigid not easy for Modification build in static function block Library |
| 5 | Scalability | Scalable depends on architecture Design | Design for Scalability |
| 6 | Cost | Cheaper compare to DCS | Expensive Compare to PLC |
| 7 | Complexity | Could be very Simple to very Complex | Plenty of Library . Things are design for Simplicity |
| 8 | Skills Needed | Ladder Logic, Structure Text, Function Block, Sequential Function , C,J | Function Block, NT, SQL |
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PLC versus DCS ( Control Architecture /Communication Protocol )
| Hardware | >Allen Bradley | >Siemens | ||||
| ControlLogix | CompactLogix | S7 1500 | S7 1200 | Simatic HA Series | Simatic RTU | |
| Functionality Configuration | PLC / DCS/ Telemetry | PLC / DCS/ Telemetry | PLC / DCS/ Telemetry | PLC / DCS/ Telemetry | DCS Main Batch Controller | Telemetry |
| Redundancy | Auto Triger | User Configured | Auto Switch FB | User Configured | Batch Control Take Over | No Redundancy |
| TCP/IP | Yes | Yes | Yes | Yes | Yes | Yes |
| Modbus | Yes | Yes | Yes | Yes | Yes | YEs |
| Profibus | No | No | Yes | Yes | Yes | Yes |
| Profinet | No | No | Yes | Yes | Yes | Yes |
| Control Net | Yes | Yes | No | No | No | No |
| FieldBus | Yes | Yes | Yes | Yes | Yes | No |
| Hart | Yes | Yes | Yes | Yes | Yes | Yes |
| Processing Power | High Processing Power | Medium Processing Power | High Processing Power | Medium Processing Power | High Processing Power | Medium Processing Power |
PLC versus DCS ( Implementation and Utilization )
| Hardware | >Allen Bradley | >Siemens | ||||
| ControlLogix | CompactLogix | S7 1500 | S7 1200 | Simatic HA Series | Simatic RTU | |
| DCS Utillization | PlantPax Connected Enterprise | No | No | No | Sinema Server Connect | No |
| Telemetry | Yes | Yes | Siemens Remote
Access |
Sinema Remote
Sccess |
No | Yes |
| Certification Max | Sil2 Sil3 | Sil2 | Sil3 | Sil2 | Not Clear | Not clear |
| Utilization Market Leader | Onshore Chemical Process Plant | High speed Manufacturing Plant | Water Treatment Plant & Pharma FMCO | Processing Plant | Chemical and Food Plant | Wind Farm |