Restart after power outage

[faehigkeit1]

Thanks for all the input. What about using a pulse timer that after power comes back on, wait maybe 30sec. and then a 1sec pulse to simulate pushing the start button
Thanks again everybody
Dean

 

[MASEngr]

The system I'm working on goes to a "stopped" stage when it is powered up and when estop is pressed*. No motors are on, no motion is possible. To get out of that stage, you have to unlock a cabinet then turn a keyed switch. I want to make sure it's safe to use before someone can use it.

*For the record, estop is wired to shut off the motor contactor directly (via relays), without PLC involvement. The PLC just monitors the line to detect that estop has just happened.

 

[Outrage]

Thanks for all the input. What about using a pulse timer that after power comes back on, wait maybe 30sec. and then a 1sec pulse to simulate pushing the start button
Thanks again everybody
Dean

Yes this would be a good way of performing a reset, We use a timer connected to a phase failure relay to restart automatic plant at our unmanned Waste water plants.

As mentioned below you need to consider that the pump could be off for two reasons:

1. because you switched the pump off at the push button because it wasn't required at that time perhaps because the sump etc was empty - NOT for maintenance as you should have isolated and tagged out.

2. because the power was lost.

If you loose the power it will restart in both cases and perhaps run dry damaging the pump. You need to have a system of work in place to prevent this. As suggested earlier and On-Off-Auto switch may be useful.

Cheers,

Lee

edited since rereading the initial posts.

 

[rta53]

Thats what we do for our compressors, cooling towers, and chillers - but they all have a PLC on them.

When power is restored the PLC first ascertains if it was running when the power went off. If it was then it performs a series of checks to make sure it's OK to restart (fluid levels OK, all phases present, an anti-short cycle check if a chiller, etc.) If everything is OK then the equipment restarts. The utility equipment over which we have control all have different time delays on restarting so we don't have a start up surge at the main gear. Some utility equipment is dependent on other utility eqipment, eg, chillers are depenednt on the cooling tower - which affects the start up delay times.

My apologies for bringing up this issue again but I have a situation like the OP of this thread. Don't really want to get into the pro/cons of whether equipment should be restarted after a power outage. I need to restart a pump automatically after a power outage and I was particularly interested in TConnolly's statement that "When power is restored the PLC first ascertains if it was running when the power went off". Were you referring to whether the PLC was running or the particular equipment? In my case I would only want to restart the pump if it was running when the power was lost. The pump is controlled from a Flex I/O rack connected to a SLC 5/05. At the pump there is a HOA switch and and start/stop buttons. At the MCP there is another set of start/stop buttons. What would be a good way to monitor or ascertain if the pump was running when the power failed and then use that information as a condition for restarting the pump. We are monitoring the pressure and flow from the pump, plus aux. contacts from the motor starter that provides run status.

As an aside, the SLC instruction help file says that latched outputs retain their status during a power loss. This must apply to real world outputs and not memory bits. Is this the case?

 

[adel1961]

and also ,if there is a pinch point somewhere ,you can add a small light curtain with a manual restart safety relay , so in case some one there ,can't start by itself and hit him or you would be responsiplw cos it is self starting and you have to concentrata of protecting the public first before getting the machine running (canadian code for health and safety)

 

[rta53]

and also ,if there is a pinch point somewhere ,you can add a small light curtain with a manual restart safety relay , so in case some one there ,can't start by itself and hit him or you would be responsiplw cos it is self starting and you have to concentrata of protecting the public first before getting the machine running (canadian code for health and safety)

I understand the safety issues with automatically restarting something after a power outage. However there are times when this is necessary. In my case it invloves an enclosed water pump that has no exposed moving parts and is pumping water through a closed loop.