The Vital Solution Concept vs. Safety Relay

The Vital Solution offers an enhanced level of safety that conventional safety relays do not. This difference is explained below.

Diagram 1 illustrates a safety relay circuit with one E-Stop input device. This dual input safety relay monitors both the "+" and the "-" inputs for any change in state. If either of these inputs open, the relay output contacts will open stopping the machine. Although this is dual channel and we are relying on redundancy, there are certain conditions that can occur resulting in an unsafe condition.

Diagram 1

Diagram 2 introduces a short circuit in the "+" input. Because of the dual inputs the safety relay would still stop the machine when the E-Stop is depressed and further more would not reset because the safety relay only had the "-" input open. In a failure like this we must begin to troubleshoot, by simply cycling the power to the safety relay or replacement of the relay this short circuit in the "+" input will be masked and remain in the circuit allowing the machine to operate. By re-powering a safety relay, it will see the closed inputs as normal.

Diagram 2

Diagram 3 introduces a second short across the "-" input. It is quite easy to understand that whatever caused the short circuit in the "+" input could cause a second short in the "-" input. This could be a result of crushed wires, damaged wires while being pulled through conduit, heat, or chemically damaged insulation on input wiring. In this case, when the E-Stop is depressed, nothing would happen! These short circuits have removed the E-Stop from the circuit. As a result, the machine would not stop resulting in a possible injury.

Diagram 3

Diagram 4 illustrates a very common safety circuit with two door input switches. Because of the added cost for safety relays, it is quite common to see more than one safety switch in series to one safety relay. The introduction of the short circuit in red produces a new problem. Not only can you reset the relay by replacing or cycling power, you can simply fool it by cycling door #2; thus allowing the machine to run with this short circuit in place.

Diagram 4

Diagram 5 illustrates the addition of a second short circuit. As explained earlier, this short is quite possible due to the fact that the interface between the switches could be damaged. Now both contacts of Door #1 have been bypassed. Someone entering at this door is no longer protected because the safety relay would not see this gate open, nor would it know that there are short circuits. Imagine if this was a robot cell, the robot was paused, and the operator thought it was stopped.

Diagram 5

Why the Vital Solution is changing the way people think about safety!

The difference between a standard safety relay and the Vital Solution is the dynamic signal that Vital produces. This signal is monitored throughout the system. Cycling the power or replacing the Vital controller will not result in the masking of a short circuit.

Diagram 6 illustrates the Vital Controller with two (2) doors. We have now introduced two Eden non-contact door safety sensors. These sensors are not magnetic; they are designed to work with the dynamic signal produced by the Vital. The Vital controller sends the signal to the Adam at door #2, it is altered by the presence of Eva and then sent on to the next-door where again this process takes place. Finally, the Vital received back the proper signal allowing the machine to operate. Opening either door results in the stopping of the machine.

Diagram 6

Diagram 7 introduces a short illustrated in red. Unlike the safety relay examples above, this fault would be recognized immediately! Opening door #1 or door #2, cycling power, or replacing the Vital controller would not correct this problem, therefore increasing the safety circuit of the machine. In this case, the Vital controller does not see the correct signal and therefore would not operate until the short circuit has been corrected.

Diagram 7