IN2 Access & Control's Director, Kane Tetley, was recently asked whether he would use a Cat. 2 or Cat 3. controller on an install. Read on to find out his response to this common question.
I was recently asked a very integral question; would I use a Cat. 2 or Cat. 3 controller on an install? My initial thought was that my decision is dependant on the outcome of a risk assessment, but instead, this time I asked: 'Do you understand the limitation of Cat. 2 or Cat. 3 devices?' This led to further questioning.
1) Do you have a long cable running between the Cat. 2 device and drive controller?
If yes, then a Cat. 2 device would be my choice, as the Cat. 2 controller and wiring would be checked back to the control panel.
When Cat. 3* controllers do not monitor the outputs, there is a vulnerability between the Cat. 3 controller and drive unit. As most Cat. 3 controllers use a double redundancy function to achieve Cat. 3, if a short circuit was to happen on the output, it would go undetected.
*Bircher Reglomat's Intra 6.3 and ES Gate 3 monitor the output when an edge is activated and switch both outputs if a fault is detected.
2) If the gate controller only has one input and you need to series up the controller’s outputs, or, connect more than one tested input in series, then reduce the connections or use a Cat. 3 controller.
As long as one of the outputs switches, the drive controller will not detect if a short circuit on the other series outputs is present, thus, accidentally defeating the Cat. 2 monitoring.
3) From your risk assessment, how likely is that accident to happen between a test cycle?
If it is highly likely, then a Cat. 3 controller or dead man operation should be considered.
Along with designing out as many hazards as possible during the design phase, understanding the limitations of the products is the next item on the agenda.