The 4-20 mA output, which jumps from high to low current when the MIN or MAX point level is reached, can be connected directly to a safety PLC or similar system for MIN and MAX safety applications up to SIL 3. 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 SIL 3 requirements in accordance with IEC 61508, IEC 61511-1, ISA 84-1 and DIN EN ISO 13849. Built-in diagnostics monitor the tuning fork-type sensor for damage, corrosion, material buildup 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 ºF (-60 to 280 ºC), 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.
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