Point Level Switches Include Built-In Diagnostics
Endress+Hauser introduces the Liquiphant FailSafe FTL8x series of point level switches. The level switches have two relay outputs, a 4-20mA output that connects to a failsafe switching unit with a two-channel output, safety contacts and a safety locking function.
The 4-20mA output can be connected directly to a safety PLC or similar system for minimum and maximum safety applications up to SIL3. The 4-20mA signal jumps from high to low current when the minimum or maximum point level is reached for reliable detection by the safety system. In addition, a permanent live signal of 0.25 Hz is superimposed on the sensor output to indicate the sensor is operating in the “good” state. The level switch meets SIL3 requirements in accordance with IEC 61508, IEC 61511-1, ISA 84-1 and DIN EN ISO 13849.
For high reliability, built-in diagnostics monitor the tuning fork-type sensor for damage, corrosion, material build-up and mechanical blocking. If a problem occurs, the live signal changes to notify the operator, a fault relay sends a signal to an annunciator or PLC, and a combination of three LEDs on the housing indicate the problem so that the switch can be cleaned, repaired or replaced prior to failure.
The switches can be used for minimum and maximum level detection in liquids from -76 to 536 F (-60 to 280 C), at pressures up to 1450 psi (100 bar), viscosity up to 10,000 mPa-s, and densities from 0.4 to 2.0 g/cm3. The FTL8x can also be used in highly corrosive media.