User Tools

Site Tools

Trace:

Differences

This shows you the differences between two versions of the page.

Link to this comparison view

Both sides previous revision Previous revision
Next revision
Previous revision
thermistor_troubleshooting [2016/04/16 16:54]
Traumflug [Check Voltage on the Processor Pin]
thermistor_troubleshooting [2018/05/27 16:10] (current)
Line 13: Line 13:
   * //CT1// means to smooth out noise, it's not directly involved in the measurement circuitry.   * //CT1// means to smooth out noise, it's not directly involved in the measurement circuitry.
   * //​Connector//​ is where the thermistor is connected.   * //​Connector//​ is where the thermistor is connected.
-  * //RT1// makes up a [[https://​en.wikipedia.org/​wiki/​Voltage_divider|voltage divider]] together with the thermistor.+  * //RT1// makes up a [[https://​en.wikipedia.org/​wiki/​Voltage_divider|voltage divider]] together with the thermistor. Most controllers have a 4700\_ohms resistor here, which gives optimum resolution at about 100\_°C. 1000\_ohms moves the range of optimum resolution closer to typical extruder temperatures.
  
-Connecting components this way gives a voltage on the signal line which depends on the thermistor'​s resistance and accordingly,​ on the thermistor'​s temperature. If the thermistor is very hot, its resistance is near zero, so the signal'​s voltage will be close to zero. If the thermistor is very cold resistance is very high, signal'​s voltage will beclose to the supplied voltage, 3.3\_volts (or 5\_volts on other controllers). In between is our measurement range.+Connecting components this way gives a voltage on the signal line which depends on the thermistor'​s resistance and accordingly,​ on the thermistor'​s temperature. If the thermistor is very hot, its resistance is near zero, so the signal'​s voltage will be close to zero. If the thermistor is very coldresistance is very high, signal'​s voltage will beclose to the supplied voltage, 3.3\_volts (or 5\_volts on other controllers). In between is our measurement range.
  
 ===== Hardware Measurements ===== ===== Hardware Measurements =====
Line 21: Line 21:
 Before searching for firmware misconfigurations,​ it's always a good idea to check hardware. A firmware can only report the voltage on the processor'​s signal pin. Before searching for firmware misconfigurations,​ it's always a good idea to check hardware. A firmware can only report the voltage on the processor'​s signal pin.
  
 +==== Thermistor Type ====
 +
 +Actually, thermistor type doesn'​t matter much for troubleshooting. They all work by the same principle, so the circuitry shown above always works (unless it's broken). Most RepRap printers use thermistors with 100\_kOhms nominal resistance. This means they have 100\_kOhms at 25\_°C ("room temperature"​).
 +
 +During firmware configuration types matter a lot more, because there we want not only a working principle, but also reasonably accurate readings.
 ==== Check Supply Voltage ==== ==== Check Supply Voltage ====
  
-Easiest way to do this is to disconnect the thermistor and measure voltage between both pins. With no thermistor connected, it should be full supply voltage, 3.3\_or 5\_volts depending on the controller.+Easiest way to do this is to disconnect the thermistor and measure voltage between both pins on the board. With no thermistor connected, it should be full supply voltage, 3.3\_or 5\_volts depending on the controller.
  
 ==== Check Thermistor Wiring ==== ==== Check Thermistor Wiring ====
  
-This measurement is simple, too. Disconnect ​the thermistor and measure resistance between both pins. At room temperature this should be around the nominal value of the thermistor, typically 10\_kOhms or 100\_kOhms. Warming the thermistor by hand should reduce this resistance.+This measurement is simple, too. Unplug ​the thermistor ​connector ​and measure resistance between both pins there. At room temperature this should be around the nominal value of the thermistor, typically 10\_kOhms or 100\_kOhms. Warming the thermistor by hand should reduce this resistance ​by a few kOhms.
  
 Measuring the thermistor while it's plugged in gives false results. Measuring the thermistor while it's plugged in gives false results.
Line 41: Line 46:
 This measurement can be done without the processor installed. If one is installed, the firmware shouldn'​t make these pins an output, but keep the default, input. This measurement can be done without the processor installed. If one is installed, the firmware shouldn'​t make these pins an output, but keep the default, input.
  
-Without a thermistor connected, both pins should read full 3.3\_volts (5\_volts on 5\_V controllers). Connecting a thermistor at room temperature should drop this not much, but a bit. Typically to 3.2\_... 3.3\_volts.+Without a thermistor connected, both pins should read full 3.3\_volts (5\_volts on 5\_V controllers). Connecting a thermistor at room temperature ​(not to these processor pins, but to the thermistor header on the board) ​should drop this not much, but a bit. Typically to 3.1\_... 3.2\_volts.
  
-Warming the thermistor by hand might change that slightly, perhaps by another 0.05\_V drop. Warming the thermistor with a lighter (be careful to not overheat it!), should drop that voltage further, down to very low readings, like 0.5\_V.+Warming the thermistor by hand might change that slightly, perhaps by another 0.05\_V drop. Warming the thermistor with a lighter ​or soldering iron (be careful to not overheat it!), should drop that voltage further, down to very low readings, like 0.5\_V.
thermistor_troubleshooting.1460818442.txt.gz · Last modified: 2018/05/27 16:10 (external edit)