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E-direct complements our traditional offering by providing you with a quick, effective way to purchase easy-to-configure, entry-level instrumentation.

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Limit switch

Contactor with loop power supply for monitoring current or voltage signals

  • Limit switch RTA421 ©Endress+Hauser

The RTA421 contactor monitors industrial processes for safe operation. The unit analyzes current (0/4...20 mA) and voltage signals (0/2...10 V) and switches two independent output relays if the values either exceed or undercut the preset alarm set points. On the display both limit values are indicated in parallel. The bar graph informs on the connected signal at any time. Applications include pump control in the waste water industry. Level measurement in silos can be economically achieved.


  • 2 relays for set point monitoring (with SPDT contacts)

  • Loop power supply for connected sensors

  • LC display for alarm set points and bar graph

  • Compact housing

  • Front end setup using 3 push buttons

  • DIN rail mounting, 45 mm housing width

Field of application

  • Plant and machine construction

  • Panel builders

  • Process monitoring

  • Process control

Features and specifications

Documents / Manuals / Software

Accessories / Spare parts

Predecessor / Successor

Predecessor: HTA182, HTA380, HTA423, XT170


PT Endress+Hauser Indonesia
Multika Building, 3rd Floor Jl. Mampang Prapatan Raya no. 71-73 Jakarta Selatan , 12790 Indonesia
Tel.: +62 21 797 5083
Fax: +62 21 797 5089