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pt100 [2017/01/25 15:45]
arthur
pt100 [2019/02/22 04:01] (current)
50.25.223.35 Cleaned up phrasing/grammar, added some missing articles.
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-== PT100 configuration ​and usage+A [[https://​en.wikipedia.org/​wiki/​Resistance_thermometer|PT100]] is a commonly used RTD. Compared to NTC (the most common) thermistors work, the PT100 is "​PTC"​ so the change in resistance with temperature is "other way around"​. (PT100'​s also have a very different curve than NTCs handled by Thermistor class.) 
 + 
 +"​PTC"​ means "​positive temperature coefficient"​ so electrical resistance increases with raising temperature. They cannot be used as-is, you must use an amplifier circuit to raise the voltage change so they become usable by SmoothieBoard. 
 + 
 +Currently Smoothie only supports E3D's PT100 amplifier board. Other PT100 amplifiers may be supported later (i.e. MAX31865 via SPI). 
 + 
 +<callout type="​danger"​ icon="​true">​ 
 +The PT100 E3D amplifier needs to be powered from the AVCC and AGND header pins on the SmoothieBoard,​ only newer boards have this header. 
 + 
 +If you do not have AVCC/AGND pins, you can use 3.3V and GND. However this may introduce noise in the ADC system and may affect all temperature readings from analog sources (i.e. thermistors and PT100). 
 + 
 +**DO NOT power from 5v or you will kill the port.** 
 +</​callout>​ 
 + 
 +You wire a PT100 //almost// the same way you would a thermistor, but you need to specify to Smoothie it is a PT100 and where you connected the amplifier signal output: 
 + 
 +<​code>​ 
 +temperature_control.hotend.enable ​             true 
 +temperature_control.hotend.sensor ​             pt100_e3d 
 +temperature_control.hotend.e3d_amplifier_pin ​  ​1.30 ​       # must be a free ADC pin, not a temperature input 
 +</​code>​ 
 + 
 +<callout type="​info"​ icon="​true">​ 
 +When using a PT100 sensor type you do not need to set values for the thermistor kind or thermistor_pin. If you do, these values will be ignored. 
 +</​callout>​ 
 + 
 +<callout type="​danger"​ icon="​true">​ 
 +You **must** use a spare ADC pin to connect the amplifier signal; you **cannot** use a thermistor input due to the pull-up that is already on the board. On most boards that means either 1.30 or 1.31, depending on what is more convenient. 
 +</​callout>​