Dead Man’s Switch – The Electrical One…

While a Google search of “dead mans switch” brings with it a host of interesting non-engineering references, we concern ourselves today with the ones related to the more pedestrian and technical meaning:  Operator Presence Detection.

The phrase “Dead Man’s Switch” was originally coined by engineers at the turn of the century who were running electric streetcars and trains. These devices do pretty much what the name implies: they prevent a disaster if the equipment operator suddenly dies or becomes incapacitated.  Indeed, deployment of dead-man devices in the USA saw great increase after the famous Malbone Street Subway Crash in Brooklyn in 1918 which killed over 70 people. Today throughout the world, trains and rail transit vehicles universally employ these devices.

In more civilized society, this application is commonly called “Operator presence detection”, and these switch based devices are used on a wide variety of equipment as fail-safe mechanism. When the fail-safe condition is detected the make or break of the circuit is designed to bring operation back to a safe state such as reducing motor idle speed, applying brakes, or sounding alarms.

Applications of Operator Presence Detection

At CPI, we’ve seen variations of our E1 limit switches used in a wide variety of these fail-safe applications.

  • Handle mounted on vehicles for “lost grip” detection. Our line of pendant switches has the low profile options and environmental durability to withstand abusive usage.
  • Hand held tools and lawn and garden equipment – Typically when saws or rotating blades are involved operator presence is required. In fact every walk-behind mower sold in the US since 1982 has an operator-presence control, which by law must stop the blades within 3 seconds after the user lets go of the controls.
  • Touch Sensor backup switch – Capacitive touch sensor switches detect a driver’s hand except where the driver needs gloves or the sensor fails. In those cases a backup dead man’s switch is provided that can use our standard, high reliability, E1 Safety Limit Switch.
  • Seat Switches – a very common application for our E1 Limit switch is in “operator-in-seat” type applications on lawn mowers, combines, tractors, you name it. One large mower manufacturer uses our CPI E1115 that is commonly employed in this application.
  • Pedal Switches – This application is similar in use to handle mounted where release of the pedal constitutes an emergency event on trains typically. The CPI switch is ideal for these applications due to its small form factor and extremely high reliability and durability.

Features of CPI Switches for Operator Presence Detection and General Fail-Safe Applications

A few primary factors bring equipment manufactures to our door time and time again for dead man switch and indeed many general fail-safe switch applications:

  1. Outdoor Environmental Durability. Resistant to sand, wind, dirt, mud and vibration. And of course our switches are completely, 100% waterproof, not spalshproof or water resistant.
  2. Versatile, and low profile form factors with sealed versions tolerating extreme temperature ranges.
  3. Long electromechanical endurance means no in-warranty service issues.

Switches Commonly Used in Fail-Safe Applications

E1115CPI E1115 – This is a commonly used low profile switch bracket with a “simulated” roller, ideal for under the seat applications.  As such it is unobtrusive making for good ergonomics at the seat. The switch itself can be specified in a wide variety of standard electrical configurations and lead lengths.

 

 

CPI’s E1134 Interlock Limit SwitchCPI E1134Roller Level Flush Mount switch. Similar to above but with a hard nylon roller. Parameters such as travel length, current rating, and electromechanical endurance are customizable. CPI has achieved endurance qualifications over 5 million cycles with this basic roller limit switch design.

 

 

 

E1085CPI E1085 – This is a Flush mount bracket on a “dual switch” configuration allowing two separate circuits to be controlled during a fail-safe event. All the same comments with regard to switch customization and electrical parameters apply, but to both switches.

 

 

Here are some useful links:

CPI Will Help You Select a Switch that’s Right for Your Application

At CPI we’ve been making high endurance waterproof switches for over 70 years from our factory here in East Hanover New Jersey. We’ve made switches for US Military Vehicles, Navy Ships, and Construction Vehicles, not to mention pleasure boats, lawn mowers, and even mountain bike racers.

When companies get fed up with the performance of a cheap, offshore-made switch in a critical application, they typically come to us.  In production quantities our prices are competitive with the offshore guys, but with none of the field problems.  Our engineers see to that during a rigorous qualification of switches which are made right here in the USA. With CPI you have both off-the-shelf and full custom options for your switch design.

Call us today.  Make the switch to CPI.

http://cpi-nj.com