J. Kissel

Recall there is an analog TEST voltage input to the OMC DCPD in-vacuum transimpedance amplifier TIA (D2000592), whose in-air interface is through the OMC DCPD Whitening Chassis' (D2200215) J4 D9M port labeled "From AI/DAC / Test Inputs." This whitening chassis lives in U24 of ISC-R5 by HAM6.
 port. This port usually connected to a DAC via cable ISC_444, and the DAC channels can be used to test the response of the TIA / Whitening / AA / ADC chain entirely remotely.

However, these test inputs are not always engaged and functional; they are governed by analog relay switches. These relay switches themselves are governed by digital binary input, generated by the Beckhoff slow-controls system.

This is aLOG is about how to find and use these relay switches.

It's been a while since I used this screen (July 2023; LHO:71225), and it looked different than I remember and can't find an aLOG about the change, so I document it here.

See attached screenshot.
What's shown as "A_Relayset & B_Relayset" are the settings channels H1:OMC-DCPD_A_RELAYSET and H1:OMC-DCPD_B_RELAYSET.
Setting these to "On" or "1.0" turns ON the relay enabling the test input excitation.
Setting these to "Off" or "0.0" turns OFF the relay disabling the test input excitation.
In the screenshot, the A channel relayset is called out with a deep purple arrow.

What's shown as "A_Relaytoggle" & "B_Relaytoggle" are momentary channels H1:OMC-DCPD_A_RELAYTOGGLE and H1:OMC-DCPD_B_RELAYTOGGLE.
These are momentary channels, that if set to "On" or "1.0," it toggles the RELAYSET to the opposite setting it's currently in, and then self-restores to "Off" or "0.0." 
So, on the screen, hitting "On" changes the relay state, and hitting "Off" does nothing.
In the screenshot, the A channel relaytoggle is called out with a dark green arrow.

Note -- there is only one differential test input from the J4 D9M, "From AI/DAC" port of the whitening chassis. So if you turn on BOTH A and B test input relays, it drives BOTH A and B's test inputs simultaneously with signal identical to the input. If you want, or only need to, drive one DCPD's TIA path at time, then turn on only that corresponding relay.