Network problems with ISD400-7xx1 switched off

Problem description:

When the supply voltage of an ISD400-7xx1 (red laser) is switched off, it can happen that the associated ISD400-7xx2 (infrared laser) causes network problems. These can be, for example, communication errors, connection timeouts or complete crashes in the network due to an unwanted network loop, which can be generated by the ISD400-7xx2. The effect described only occurs if the distance between the two ISD400 is small (typically up to a few meters apart). If the network cable is removed from the ISD400-7xx2 or the light path between the two ISDs is interrupted by hand, for example, the problems disappear.

Cause:

Regardless of the operating mode of the opposite ISD400-7xx1, a small part of the infrared light emitted by the ISD400-7xx2 is reflected back onto the own receiver lens by the "passive" optics components (screen, receiving diode, lens etc.) of opposite device. To block this unwanted infrared signal, there is an optical bandpass filter in the receiver path of the ISD400-7xx2. We have found that the tolerance of the installed filters is sometimes too large and therefore the infrared light is not sufficiently blocked. This causes the infrared device to send its own transmission signal back to the connected network, which can lead to the network problems mentioned.

If the ISD400-7xx1 is not switched off, there is no problem, as the received red light intensity of the useful signal at the ISD400-7xx2 is significantly higher than the unwanted own infrared intensity of the interfering signal. There is also no problem in the other direction if not the ISD400-7xx1 but the ISD400-7xx2 is switched off.

Possible solution:

1. Switch off the laser of the ISD400-7xx2 via MF input as long as the ISD400-7xx1 is de-energized.

2. When using the ISD400 Pro on a vehicle that is temporarily switched off, you should mount the ISD400-7xx2 on it and the ISD400-7xx1 on the opposite fixed side, if this is possible in relation to a DL100 Pro distance laser that may be installed in parallel. Details on minimum mounting distances regarding interference for different installation situations can be found in the operating instructions for the DL100 Pro or ISD400 Pro.

3. Return the ISD400-7xx2 to our repair department and note in the paperwork that the device is to be replaced with a device with an improved optical filter.

Note:

The changeover of series production to new bandpass filters took place with calendar week CW11 of 2025. Therefore ISD400-7xx2 with serial number >=2511xxxx are no longer affected by the self-blinding problem.