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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Detailed 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.


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

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


Datalogger Considerations

Compatible Contemporary Dataloggers (SDI-12)

CR200(X) Series CR800/CR850 CR1000 CR3000 CR9000X CR300 Series CR6

Compatible Retired Dataloggers (SDI-12)

CR500 CR510 CR10 CR10X 21X CR23X CR5000 CR7X CR9000


LR4 OS v.1.3 (46 KB) 08-13-2014

Current LR4 firmware. Read the manual for the update procedure.

View Update History

Frequently Asked Questions

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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