MTL Barries - MTL7796 - - Vibration probes

The MTL7796- is an intrinsically safe (IS) shunt-diode safety barrier that uses zener diodes to limit the amount of energy that can be transferred to a hazardous area, preventing ignition. It is configured for a 28V supply and a negative polarity, designed to work with 3-wire vibration monitoring transmitters. The barrier keeps the voltage and current in a hazardous area below the level required to cause a spark that could ignite a flammable atmosphere

Working principle

• Energy Limitation: The MTL7796- uses zener diodes to clamp the voltage and resistors to limit the current flowing to the hazardous area.
• Fault Protection: In the event of a fault, such as an overvoltage in the safe area, the zener diodes conduct, and the barrier's internal or replaceable fuse blows, disconnecting the hazardous area from the fault and stopping the energy transfer.
• Intrinsically Safe Design: This "intrinsic safety" technique prevents an explosion rather than containing it, as the amount of electrical energy is always kept below the ignition energy level.
• 3-Wire Transmitter Compatibility: The MTL7796- is specifically designed for 3-wire transmitters, like those used for vibration monitoring, which require a separate power input.
• Installation: It is a DIN-rail-mountable barrier with removable terminals for easy installation, maintenance, and providing a "loop disconnect" by unplugging the terminals, which helps during commissioning or fault-finding.
• Polarity: The "negative polarity" design means the hazardous area side of the barrier is connected to the negative side of the power supply

The MTL7796- is an intrinsically safe shunt-diode barrier that operates by limiting the electrical energy transferred between a safe area and a hazardous area to a level that is too low to ignite a flammable atmosphere.

Vibration probes

Working Principle

The primary principle of the MTL7796- (and all shunt-diode safety barriers) is intrinsic safety (IS). This technique prevents explosions by ensuring that no spark or hot surface capable of igniting a potentially explosive atmosphere can occur, even under fault conditions.
The working principle relies on a simple, robust passive circuit design featuring three main components: zener diodes, series resistors, and a fuse.

1. Zener Diodes: These diodes are connected in shunt (parallel) across the positive and negative lines of the circuit, and also to a dedicated, high-integrity safety earth connection. If the voltage in the safe-area circuit rises to an unsafe level (e.g., due to a power supply fault or transient voltage surge), the zener diodes conduct, diverting the excess voltage safely to the earth.
2. Series Resistors: These resistors limit the current flowing into the hazardous area under normal and fault conditions, even if the zener diodes are activated.
3. Fuse: A fuse provides protection against sustained overcurrents. In the event of a persistent high-voltage fault, the fuse will blow, permanently breaking the connection and preventing further energy transfer into the hazardous area.

Function and Application

The MTL7796- specifically provides intrinsic safety for vibration probes

• It acts as a passive interface, meaning it is a simple, unpowered component that does not amplify signals or provide additional relay functions like active isolators do.
• It is designed for DIN-rail mounting and uses removable terminals for ease of installation and maintenance.
• Hazardous-area terminals are identified by blue labels to prevent wiring errors.

By employing this method, the barrier ensures that the energy levels in the hazardous area remain below the minimum ignition energy (MIE) of the surrounding flammable gases or dusts.

 Full Datasheet