Thermocouple wiring which already includes amplification circuit

[VirtualBrown]

@dc42 reading about the chip which seems to be an Analog Devices AD8495, I’m probably missing the 5 V supply to this daughter board which would explain the 2 ways on the ribbon cable which are connected together on the old motherboard before I loose track of them. Where on the Duet 3 Mini would be best to take a 5V supply?

I was planning on adding some LEDs in the future so would like to leave the NEOPIXEL socket free.

[Phaedrux]

Perhaps the paneldue connector if you're not using one.

https://docs.duet3d.com/duet_boards/duet_3_mini_5_plus/duet_3_mini_5+_wiring_v0.5_v1.0_v1.01.png

[dc42]

@virtualbrown all the 5-pin IO connectors on the Duet 3 Mini have 5V.

[VirtualBrown]

@dc42 thanks, any idea on those values for Bxxx and Cyyy?

[VirtualBrown]

@dc42 i get an error: VSSA fault when connecting that wire to 5 V so that much not be correct.

Struggling to work it out as the extruder temperature reading doesn’t respond to heat in the extruder, so something must be missing.

[dc42]

@virtualbrown said in Thermocouple wiring which already includes amplification circuit:

@dc42 i get an error: VSSA fault when connecting that wire to 5 V so that much not be correct.

That error suggests that you have connected the VSSA pin of the TEMP connector you are using to 5V.

[VirtualBrown]

@dc42 so there are 4 ways of the ribbon cable used for the temperature sensor. 2 of which are connected together, so we have 3 discrete connections. Any idea which is which? Do the photos above shed any light?

[dc42]

@virtualbrown from the amplifier there will be a +5V connection, a ground connection, and an output connection. Connect the 5V and ground connections to 5V and GND respectively on an IO_ connector. Connect the amplifier output to the THERM pin (not the VSSA pin) of a temperature input connector.

[dc42]

PS - I think the correct parameters for the M308 command to configure the linear analog sensor are 0 for the lower limit and 330 for the upper limit.

[VirtualBrown]

@dc42 she lives!!

Now I just need to fine tune those B and C values. I’ve got a multimeter thermocouple attached to the heater block. Is there a methodical approach to adjusting each value?

Its currently saying 19 degC when the multimeter says 33.

[dc42]

@virtualbrown the B value affects the reading when the thermocouple temperature is close to zero, and the C value when it is much higher. So I suggest you adjust B to get a good reading at room temperature, then adjust C to get a good reading at printing temperature. You may need to repeat this a few times.

Alternatively, use your multimeter to measure the output of the amplifier at room temperature and at printing temperature. Then extrapolate those values to calculate the temperature at zero output and the temperature at 3.3V output.

[VirtualBrown]

@dc42 I found B0 and C500 work well.

Thank very much for all your help on this!