OptoNews: Tech tip - Just 2 wires to your dry contact switch

Posted by Jean Femia on Apr 15, 2015 5:15:00 PM

SNAP-IDC5-SW digital input moduleSay you've got a dry contact switch you want to monitor so you know when it's closed. Could be a level sensor or pressure indicator, a magnetic reed switch or snap-action micro switch, or maybe a relay contact.

There are lots of ways you could do that, but often the best way is to use a SNAP-IDC5-SW digital input module. Why?

  • It supplies 15 volts of power to an external dry contact switch.
  • You only need 2 wires to connect the switch to the module.
  • You can monitor 4 switches from 1 module.

Ben Orchard raves about this module in his recent blog post on monitoring water usage, and with good reason: it makes life easier by saving wiring time and complexity.

Two versions of this module are available:

  • The SNAP-IDC5-SW is for normally open switches and senses switch closure.
  • Its mate, the SNAP-IDC5-SW-NC, is for normally closed switches and senses when they open. 

Let's take a look at the difference between wiring a switch to the workhorse module SNAP-IDC5, versus wiring it to a SNAP-IDC5-SW.

Wiring a switch to a SNAP-IDC5 module

Module wiring: switch to SNAP-IDC5

To monitor a dry contact switch with a SNAP-IDC5, you need to provide a power supply. Many power supplies aren't current or voltage limited, so to guard against failure or fire in the case of a short, you also need to add a suitable fuse. Wires must be properly shielded and grounded. 

Wiring a switch to a SNAP-IDC5-SW module

Module wiring: switch to SNAP-IDC5-SW

Because the module supplies power to the switch, you don't have to provide a power supply. And because each channel on the module is current-limited to 7 mA, it's safe to to use without a fuseWire the switch directly to the module using two wires. 

Wiring is much simpler. If you're in a hurry, or if labor costs for wiring are high, this module will help you. 

Will it work for you?

As always, if you have any questions about the most suitable I/O module for your application, call or email us. Pre-sales Engineering is free. 

Call: 800-321-6786 (toll-free in the U.S. and Canada) or 1+951-695-3000
Email: systemseng@opto22.com

See the SNAP-IDC5-SW         See the SNAP-IDC5-SW-NC

OptoNews April 15, 2015 - Read more in this issue:

Topics: Remote monitoring, Tips, optonews, OptoNews 2015-04-15

Written by Jean Femia

Jean Femia writes about technical subjects and has focused on automation and control systems for more than 15 years. She likes learning about technology and taking corners in her Honda S2000.
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