Redundant Temp Sensors

RedWagon

I have two PT100 temperature sensors connected to the PT100 daughter board. They both seem to work individually but I'm looking for some way to setup fault detection if the readings get too far apart. Is there a way to setup redundant temperature sensors?

RedWagon

I have gotten both sensors to show up in the web ui by assigning the extra sensor to heater 2 (no actual heater) and then add both heaters to the tool definition.

M305 P1 X200
M305 P2 X201

M563 P0 D0 H1:2 F2

This way I can see if something looks wrong but I would also like to add config to automatically shutdown if there is too much of a difference.

jens55

I too am looking to get a second sensor on my bed. I have the sensor installed but so far have not figured out how to hook it up. Thank you for posting your current setup - it will get me halfway there and I will watch this thread to see what other people have done.
I was expecting to have to wait until the new decision logic makes it into the g-code.

Veti

@RedWagon said in Redundant Temp Sensors:

way to setup fault detection

the duet implements fault detection for the heating. if the probe disconnects it will read 2000 and the heater will be faulty. if the sensor dislodges from the object where the temperature is to be measured, it will report a fault, because the temperature is not rising.

DocTrucker

@Veti they are after assigning two sensors to the same heater and defining a new heater fault condition as the temperature sensor readings being too great, be it with a measure of processing to avoid tripping on noise.

Essentially they are asking for a mirror of the Marlin feature:

TEMP_SENSOR_1_AS_REDUNDANT

Edit: to avoid "the man with two watches never knows the time" situation the primary sensor would be used for control as usual and the secondary will essentially only cause heater faults to be risen if it's temp reading is too greatly different to the primary.

dc42

You can use the M143 command to use a redundant sensor for over temperature monitoring. Note, this feature is not yet available in RepRapFirmware 3.

RedWagon

I'll setup M143 to add the over temp monitoring to both sensors. That will add some level of extra protection. During my setup and testing I can confirm that when the sensors are disconnected the readings go up to 2000.

Fault detection if the sensors get too far apart would still be a nice feature to have but it's not a blocker.

dc42

@RedWagon said in Redundant Temp Sensors:

Fault detection if the sensors get too far apart would still be a nice feature to have but it's not a blocker.

I'll add that to the firmware wishlist. It shouldn't be too difficult to add it as another M143 option.

p8blr

@dc42 Is this still in the pipeline? I've got a heater array on my print bed and have had some heaters die, so I'd like to have a thermistor on each heater. Also, is there a maximum number of thermistors (P parameter in the M143 command)?

Thanks