Though Beckhoff model was generated for the WFS DC signals, it wasn't reading anything at all.

We eventually found that the Legacy PD concentrator that routes WFS DC and PDH DC signal to Beckhoff chassis (https://dcc.ligo.org/cgi-bin/private/DocDB/ShowDocument?docid=61861) had a manufacturing error: DB37 male and female connectors are mixed up.

DB37 female should be used for the output end that is connected to Beckhoff input, but DB37 male was used instead.

Likewise, DB37 male should be used for the input end that is connected to the output of the legacy LSC diode interface, but DB37 female was used instead.

Due to this, apparently the Beckhoff cable and the legacy LSC diode cable were swapped as it's impossible to connect things up correctly.

We used two 37pin gender changers (one male-female, one female-male) to "fix" this problem. After this, it seems that the EPICS screen for WFS DC is displaying something sensible.