Understanding Zero Volt or Volt-Free Contacts: Demystifying the Terminology
There’s a common misconception surrounding the term “volt-free contact.” Even seasoned engineers sometimes grapple with its exact meaning partly due to the variety of names it goes by. In this post, we’ll dive deep into what a volt-free contact is, its applications, and why it’s essential in various industries.
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Table of Contents
What is a Volt-Free Contact?
At its core, a volt-free contact is simply an ordinary switch. Contrary to what the name might suggest, it doesn’t monitor resistance or potential in any complex manner.
It’s just a basic contact that can be used to power or control other devices but a ‘free contact’ one that is free to be used to control another circuit.
Most commonly found in relays internal to machines, the ‘free contact’ enables signals and control circuits outside of the machine to get information from it.
Different Names, Same Concept
Depending on the region or industry, a volt-free contact might be known by various names:
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- Dry contact
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- Potential-free contact
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- Zero volt contact
- Volt Free Contact
Despite the different terminologies, they all refer to the same basic concept.
Applications and Examples
One of the primary uses of volt-free contacts is within relays. For instance, in a recent example from a job we were doing inside a factory. We needed to get a signal from the X-ray device to the line control panel that the X-ray reject had been triggered.
A signal from the X-ray reject had been sent back to the line control panel using a volt-free contact. This ensures that if the X-ray detects an anomaly, the reject conveyor downstream is triggered to remove the faulty product.
Example: In a circuit board of this X-ray machine, there’s a relay for this purpose. When the X-ray machine detects a faulty product, it sends a signal ( 24 volts) to the line control panel. This signal then triggers the reject device, ensuring the faulty product is removed from the production line.
Understanding Normally Open and Normally Closed Contacts
When we are talking about volt-free contacts, there are two primary types:
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- Normally Open (NO): This type of contact is open when at rest and closes when activated. It’s often used for control signals.
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- Normally Closed (NC): This contact is closed when at rest and opens when activated. It’s typically used in safety circuits to ensure fail-safe operations.
A simple way to remember the difference between these contacts is:
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- 1 & 2: Straight through (representing NC)
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- 3 & 4: Open door (representing NO)
Safety relays, for instance, utilise volt-free contacts. These relays have safety contacts that operate on two channels, ensuring dual-channel control for enhanced safety.
Conclusion
Volt-free contacts, despite their potentially confusing name, play a crucial role in various industries. Whether it’s ensuring the safety of a production line or controlling specific devices, understanding these contacts is essential for engineers and technicians alike.
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Internal Resources for Further Reading
To further assist you in your engineering endeavors, we’ve curated a list of internal resources: