Thermisors showing wrong temperatures

[Phaedrux]

@mendelevium said in Thermisors showing wrong temperatures:

@mendelevium
Please note that I do not have a sensor daughterboard in place for the third heater.

Does that mean you have a thermocouple connected directly to the board?

Can you post a photo of your board setup?

Are you getting any heater fault messages in the console?

[mendelevium]

@mendelevium
Could someone explain how I can choose the right sensor as the heatbed has an NTC 100K thermistor and not a thermocouple.
The hot ends have a thermocouple

[Phaedrux]

@mendelevium said in Thermisors showing wrong temperatures:

@mendelevium
Could someone explain how I can choose the right sensor as the heatbed has an NTC 100K thermistor and not a thermocouple.
The hot ends have a thermocouple

M308 S0 P"bedtemp" Y"thermistor" T100000 B3950 ; configure sensor 0 as thermistor on pin bedtemp
M950 H0 C"bedheat" T0                          ; create bed heater output on bedheat and map it to sensor 0
M307 H0 B1 S1.00                               ; enable bang-bang mode for the bed heater and set PWM limit
M140 H0                                        ; map heated bed to heater 0
M143 H0 S120                                   ; set temperature limit for heater 0 to 120C

[mendelevium]

@phaedrux
I have a max31856 daughterboard

[mendelevium]

@phaedrux
No luck... the heatbed is connected to a MAX31856-based interface daughterboard. The headbed has an NTC 100k thermistor. Thank you.

[dc42]

@mendelevium said in Thermisors showing wrong temperatures:

@phaedrux
No luck... the heatbed is connected to a MAX31856-based interface daughterboard. The headbed has an NTC 100k thermistor. Thank you.

If the bed heater has a 100K thermistor then you should connect it to the bedtemp connector on the Duet, not to the daughter board. Your original line in config.g is nearly right:

M308 S0 P"bedtemp" Y"thermistor" T100000 B4138 ; configure sensor 0 as thermistor on pin bedtemp

except that B3950 is more likely to be a good match to the thermistor than B4138.

Edit: I just saw that @Phaedrux already gave you the correct config.g commands. But you still need to connect the thermistor to the bedtemp input, not the daughter board.

[mendelevium]

@dc42
So the thermistor is plugged directly into the board while the thermocouples into the daughterboard right?

[dc42]

@mendelevium said in Thermisors showing wrong temperatures:

@dc42
So the thermistor is plugged directly into the board while the thermocouples into the daughterboard right?

Yes, correct.

[mendelevium]

@dc42
Thank you the bed sensor is working and reading a reasonable temperature
the hot end temperatures are not well... One is reading 2000deg all the time. The other spikes at 2000deg for a split second then goes to a low unrealistic temperature.

[Phaedrux]

Are you using extension wires on the thermocouples?

[mendelevium]

@phaedrux
yes of course but i have over 2 m of wireing. may try to connect a thermocouple directly and see the reading...

[Phaedrux]

Thermocouples can be very particular about their wiring.

https://duet3d.dozuki.com/Wiki/Connecting_thermocouples#Section_Troubleshooting

[mendelevium]

@phaedrux
I have fitted two 0.01microfarad capacitors on each channel to earth as I had found on the forum however everything remained the same. Now I connected a new thermocouple to the board which is not touching anything and the problem remains.

[dc42]

@mendelevium,

1. Please post a photo showing the wiring between the daughter board and the thermocouple that is not connected to anything.

2. If you connect a wire link between the daughter board thermocouple terminals instead of connecting a thermocouple, what reading do you get?

[mendelevium]

@dc42
when I connected a wire link the sensor the temperature reads 23 degrees and it is not spiking.

[mendelevium]

@dc42
the problem here seems to be complex because i have built numerous 3d printers and never had this kind of issue. I have the duet fitted in a metal enclosure which has two large harting type metal clad plugs x 24 pin each. The connections from the board run to the harting around 30 cm long. The machine has two harnesses plugged into the control. The harnesses are around 1 meter long and there is around 1 to 1.5 meters of cables inside the machine. The issue is that they run along with limit switches and motor controls. So my solution is to substitute the cables of the thermocouples and with screened cables unable to pick up interference. Plus possibly also change the type of thermocouples I am using... Its a massive job to rewire and I do not want to do this in vain... What do you suggest?

[Dougal1957]

@mendelevium said in Thermisors showing wrong temperatures:

@dc42
the problem here seems to be complex because i have built numerous 3d printers and never had this kind of issue. I have the duet fitted in a metal enclosure which has two large harting type metal clad plugs x 24 pin each. The connections from the board run to the harting around 30 cm long. The machine has two harnesses plugged into the control. The harnesses are around 1 meter long and there is around 1 to 1.5 meters of cables inside the machine. The issue is that they run along with limit switches and motor controls. So my solution is to substitute the cables of the thermocouples and with screened cables unable to pick up interference. Plus possibly also change the type of thermocouples I am using... Its a massive job to rewire and I do not want to do this in vain... What do you suggest?

What sort of wire are you using to extend the thermocouples?

[dc42]

@mendelevium said in Thermisors showing wrong temperatures:

So my solution is to substitute the cables of the thermocouples and with screened cables unable to pick up interference.

Thermocouple wires carry very low voltages at low impedance. This makes them susceptible to inductive interference pickup. Screened cables are effective at shielding the cable from capacitive interference pickup, but much less effective at shielding from inductive pickup unless they are shielded twisted pair.

Thermocouple wires MUST always be twisted pair, and should be kept away from stepper motor cables. If it's impossible to keep them away from stepper motor cables, use twisted pairs for the stepper motor cables too, one pair per phase. To get accurate temperature readings, the thermocouple extension cables must be made for the same type of thermocouple wire as the thermocouple. See https://www.eurotherm.com/en/support-articles-en/traps-and-colour-confusion-in-thermocouple-wiring/.

[mendelevium]

@dougal1957
ordinary wires.... Never encountered this problem even when running S**T electronics which I would expect far more issues....

[Dougal1957]

@mendelevium See DC42's reply above I was thinking the same as he was but wasn't 100% sure.