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Topic Title: Estop Circuit over a long distance Topic Summary: Created On: 16 June 2010 09:27 AM Status: Post and Reply |
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 16 June 2010 09:27 AM
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I have a requirement to install an Estop circuit of aprroximatley 10 pushbuttons spread over a distance of 250 mtrs. I will be fitting each pushbutton with 2 contacts for one for individual indication (id which pushbutton has been activated) and one for control. My problem is Im not sure if I will have a problem with the distance using 24vdc. Any advice with possible alternatives would be of great help.
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16 June 2010 10:28 AM
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The first step will be to carry out a suitable control risk assesment to detemine what level of Estop you will require. Is a single channel enough? Do you need dual channel or dual channel with cross monitoring and protection against cable faults?
This is a brief guide from the Jokab website: http://files.jokab.com/10_web_...egory_choice_08v2.pdf It is likely that you will require some form of monitoring relay (Pilz, Guardmaster, Siemens, Dold, Jokab etc) and the manufacturers data sheets will give maximum cable lengths for the relays. All the manufacturers will give information and guides on their websites. Best regards Roger |
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16 June 2010 12:10 PM
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Many thanks Roger this is just what I was looking for.
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20 June 2010 07:20 PM
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I've not looked at the figures but can't imagine there would be any problem over 250m. The current in the button circuit of a typical safety relay is not great. The old Strowger telephone system operating at 50V operated relays located miles away.
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06 July 2010 10:57 AM
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I have worked on a few different estop circuit over long distances and have found that 24v is fine what you are suggesting. One thing to consider is the environment is going to be used in. If its going to be installed and used in a tough working environment over the years high resistances will begin to appear in the contacts. In an ideal world these will be identified and corrected however in "real world" situation we found that bumping up the voltage at output to about 26v meant that we got far longer before the resistances across the contacts dropped the voltage down to an unacceptable level.
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13 July 2010 09:19 AM
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Whenever I have used 24V over long distance, I always look to use high impedance inputs to limit the current. Use of solid state relays has allowed me to carry 24V signals over a mile around a works, with only one or 2 volts drop.
Whether this is applicable to safety circuits needs more consideration. I'd take a look for solid state safety relays or small safety PLC inputs that could be incorporated into the long distance legs of the circuit. |
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13 July 2010 07:29 PM
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After evaluation of your SIL level, with the length of run that you have I would recommend the use of a networked safety system e.g Profisafe, or similar alternative dependant on your control system, as the cost of cableing at that length would far outway the cost a digital solution.
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17 August 2010 01:02 PM
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After evaluation of your SIL level, with the length of run that you have I would recommend the use of a networked safety system e.g Profisafe, or similar alternative dependant on your control system, as the cost of cableing at that length would far outway the cost a digital solution. |
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28 October 2010 12:25 AM
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Another option is ASIsafe
Really good and cheaper than Profisafe |
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IET
» Control and automation
»
Estop Circuit over a long distance
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