Steve Kemp
Member
- Join Date
- Nov 2003
- Posts
- 122
Any thoughts on this one? I'm designing the controls for an operator-loaded, light-guard protected hydro-pneumatic press (pneum approach stroke/intensified press stroke). It's a category 4 machine, so I'm using two pneumatically series dump valves, fed via the contacts of two series-connected positively guided relays, the normally-closed contacts of which form part of the monitor reset circuit. So far, so normal. I want to monitor each of the dump valves' outputs with a pressure switch. These switches come with a changeover microswitch as standard, so I figured on using the changeover aspect to "cross-monitor" their status and incorporate this as part of the monitor reset circuit. But I figured wrong: a single c/o isn't enough, but if I use "regular" relays to expand their function, these are in themselves a source of potantial failure. I know it's only a couple of mA and relays (the ones I know) go on for ever, but it's a safety thing. All opinions welcomed. Thanks, Steve.