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I have to read six 0 - 10 V analog signals but I only have one 0 - 10 V input on the Controllino. I figure I could use six solid state relays and multiplex the signals.

When a relay is on it'll allow only one signal through then I turn it off and move on to the other signal and so on.

However, with multiple SSRs connected to the input when one analog signal changes the others also change in the same direction. I.e. if the input voltage goes up, the rest of readings also go up (though not by the same amount)

I think the output capacitance of the SSR may be affecting me here. I tried adding a pulldown resistor but that didn't work. I slowed the readings down to 2 s and that also had no effect, I imagine because the capacitance has no path to discharge.

I'm not sure how to address this (apart from not using SSRs) but I'll take any recommendations. See below for my schematic, the editor didn't have an SSR symbol so I used a regular relay.

schematic

simulate this circuit – Schematic created using CircuitLab

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    \$\begingroup\$ An analog switch IC is going to be much better for this than discrete relays. \$\endgroup\$
    – vir
    Jun 23 at 17:14
  • \$\begingroup\$ @vir do you have any recommendations? \$\endgroup\$
    – Simeon R
    Jun 23 at 17:17
  • \$\begingroup\$ I only have one 0 - 10 V input - Really? The page you linked us says two. \$\endgroup\$
    – Reinderien
    Jun 23 at 17:49
  • \$\begingroup\$ Apologies for the confusion. I only have one available* the other is already in use @Reinderien \$\endgroup\$
    – Simeon R
    Jun 23 at 17:52
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Two parameters suggest that an SSR is not a good choice for this application.

Table 1. From the datasheet.

enter image description here

An analogue switch would be a better choice. You may need to add a potential divider for each input. The CD4016 is one such device that I used 40 years ago. I'm sure there are others now.


Can you also add in an explanation as to why those parameters and their values would mean that I shouldn't use it in this application?

I don't understand the minimum load current specification myself. I would have expected the FET to behave like a resistor independent of current.

The leakage current will allow up to 1 μA through the device and this will charge up the input capacitance on your ADC.

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  • \$\begingroup\$ Thanks! Though I have a fair idea, can you also add in an explanation as to why those parameters and their values would mean that I shouldn't use it in this application? \$\endgroup\$
    – Simeon R
    Jun 23 at 17:20
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Since you're just going to an ADC, current is going to be vanishingly low so SSRs are not really a good choice. Just use a single analog mux. The one you'll likely want to use is the 4051. There are many (many) variants on the market. It's 8:1 which meets your 6-channel input requirement, and there are many incarnations which can take 20V or over.

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