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Occupancy Detection:

Lenz: LR101

Summary: The LR101 is an feedback unit for signaling purposes.

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General information
DCC Category
Occupancy Detection
Manufacturer Lenz
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Has computer interface
Firmware Upgrade Possible
Misc Details

Lenz LR101 Feedback Module

In the Digital plus feedback concept three components are combined to provide feedback on the status of the layout: Feedback encoder LR101, occupancy (current) detector LB100 and voltage monitor LB050.

The LR101 not only evaluates information from LB100s, but also information from one or more voltage monitor LB050s. If the LR101 determines, via its connection to an LB050, that voltage to the track is lost, it “freezes” the last feedback status.

A locomotive on the track is current draw. When current flows, the LB100 sends “occupied” to the LR101. If for any reason power to the track is lost, no current flows and the LB100 will report “free”, even though that does not correspond to the actual status. However, the LR101 can use the connected voltage monitor LB050 to determine that there is no power to the track. It therefore “knows” that it must not pass the incorrect “free” information from the LB100 on to the command station.

The careful combination of LR101s and LB050s prevents a loss of power or a short circuit from causing erroneous feedback to be sent to the command station.

The command station polls all connected feedback encoders LR101/100 in turn. This takes about 30 milliseconds. This polling is responded to by any LR101/100 that has had a change in status on the inputs. The information for 4 inputs at a time is sent, which requires a time of approximately 2 milliseconds. This time adds to the polling cycle. If several LR101/100 report, then the total length of the polling cycle in milliseconds can be calculated as follows:

30 + (the number of LR101/100 reporting x 2)

Already Using LR100s?

LR100s can be used together with the new LR101s. The LR100 uses two feedback addresses, while LR101 uses only one.


The LR101 has 8 feedback and one voltage monitor input. On each feedback input you can connect an occupancy detector LB100 or any other potential free (isolated) contact (such a reed switches or relays). A potential free contact is a type of switch that creates no current connections from the layout or other components of the Digital plus system to the LR101.

The input for voltage monitoring is designed solely for connecting with the voltage monitor LB050.

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