Does a relay add noise or interference to its inputs?

• Does a relay add noise or interference to its inputs?
  Posted by little_carlos on 14 Sep, 2015 12:40
• Hi, i was wondering about that yesterday and i hope you can answer this
  since the relay inputs are activated with an electromagnetic field, does that magnetic field causes any noise or interference to any signal that goes through ?
• #1 Reply
  Posted by technix on 14 Sep, 2015 12:46
• There can be some spikes if you are using stable DC to drive the solenoid but like a transformer with a thousand-turn primary and a one-turn secondary the noise is minimal.
  
  However the real concern here is contact bounce which can be significant if you bought one with unsatisfying quality.
• #2 Reply
  Posted by retrolefty on 14 Sep, 2015 19:44
• If you are asking if there is any coupling of 'noise' from coil/magnetic field to the output contacts, then no, there is no realistic concern there.
• #3 Reply
  Posted by tggzzz on 14 Sep, 2015 20:31
• Quote from: little_carlos on 14 Sep, 2015 12:40

  Hi, i was wondering about that yesterday and i hope you can answer this
  since the relay inputs are activated with an electromagnetic field, does that magnetic field causes any noise or interference to any signal that goes through ?
  

  
  Yes, repeat no.
  
  In other words it depends on the type of relay, the operational environment, and the signal.
• #4 Reply
  Posted by albert22 on 14 Sep, 2015 23:36
• 
  In this very sensitive application, some precautions in the relay were taken to prevent noise :
  http://electronicdesign.com/test-amp-measurement/whats-all-femtoampere-stuff-anyhow
  - shielding between coil and contacts
  - reduced voltage range on the coil.