LR4 4-Channel Latching-Relay Module


The LR4 relay module is useful in situations where the power is unreliable or where power needs to be conserved, because it does not need electricity to keep the relay closed. The state of the relay can only be changed by sending a command to the LR4 or by manually toggling the relay button.   

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Technical Description

Unlike traditional relays that must be continuously powered to keep their state, the LR4 mechanically latches the relay’s state allowing power to be removed. The only way to change the state of a relay is to send a command to the LR4 or to press the manual toggle button. The datalogger sends commands to the LR4 via the SDI-12 protocol or ModBus protocol.


  • Length: 17.0 cm (6.7 in)
  • Height: 6.1 cm (2.4 in)
  • Width: 3.7 cm (1.5 in)
  • Weight: 0.48 kg (1.05 lb)
  • Supply Voltage: 9 to 30 Vdc
  • Operating Temperature: -40° to +60°C
  • Relay Type: Latching
  • Maximum Voltage Ratings of Relays:
    30 Vdc/30 Vac

Power Consumption

  • Quiescent: < 2.0 mA
  • Peak: < 250 mA


  • Hardware: SDI-12, RS-232, RS-485
  • Protocol: SDI-12 Version 1.3, or ModBus via RS-232/RS-485 at 19,200 bps

Digital I/O Input Voltage

  • Maximum: +20 Vdc
  • Minimum: -12 Vdc

Relay Contacts

  • Relay #1, Relay #2: Two independent; single pole single throw (SPST)
  • Relay #3, Relay #4: Two independent; single pole double throw (SPDT)

Maximum Current

  • Relay #1, Relay #2: Not to exceed 100 VA or 5 A
  • Relay #3, Relay #4: Not to exceed 60 VA or 2 A


Please note: The following shows notable compatibility information. It is not a comprehensive list of all compatible products.


Product Compatible Note
CR1000 (retired)
CR200X (retired)
CR216X (retired)
CR5000 (retired)
CR9000X (retired)

Resources and Links

FAQs for

Number of FAQs related to LR4: 1

  1. The following relay devices can be used with the CR800 and the CR850:

    • 7321
    • A6REL-12*
    • A21REL-12
    • LR4
    • SDM-CD8S
    • SDM-CD16AC
    • SDM-CD16S

    The CR800 and the CR850 can also be used with a wide variety of third-party relay devices.

    *Because the CR800 and the CR850 only have four digital ports, they do not have the ability to switch all six of the relays on the A6REL-12.

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