Head Temperature and Humidity FAQ

Q1: What is the temperature operation range for thermal heads, and how is it controlled?

Background

There are three temperature sensors inside a TH1.x head:

• write laser diode
• head case
• board ambient

Each has different setpoints, warnings, and errors.

Write laser diode sensor

The write laser diode temperature can be checked using the command >>laser. For thermal 1.x heads, the diode temperature sensing and control is done by a hard-coded controller inside the head, not by firmware (there are no NVS parameters).

• TH1.7 (40w, water-cooled) diodes have a setpoint of 25ºC, so 24.9ºC is the temp they will try to maintain in operation. Shutdown occurs if the diode reaches 30ºC on the high end or 10ºC on the low end. Warning messages will be issued before reaching these temperatures, but no action is taken.
• TH1.0 (20w, air-cooled) uses a setpoint of 19.8ºC . The high and low points are 10ºC and 25ºC.

Head case temperature sensor

Case temperature monitoring is done with an internally mounted sensor and can be queried using the command >>head status. The NVS head parameters casehigh and caselow determine when temperature warning meassges are issued.

Note: These are just warning messages. No action is taken at these temperatures.

If temperatures reach the hard-coded limits, over-temperature error messages are issued and the diode is shut off.

• TH1.7 shuts down when the case reaches 40ºC.
• TH1.0 shuts down at 50ºC.
• Both issue an alarm and turn off the laser (or prevent it from turning on) at 10ºC.

Ambient temperature sensor

Ambient temperature error messages relate to a sensor on the main electronics board. This sensor overheating indicates a board problem or an overheated case. The PHC sensor is reported with the case temperature using the command >>head status. The hardcoded setpoint is 85ºC.

Errors

• If you get error 17742: HEAD: shutdown of thermal head due to temperature or humidity alarm then you should also check the humidity level (>>head status) to be sure that it is below the default setpoint of 30%. Maximum humidity is set with the nvs parameter head humidity.
• If you get a laser diode over-temperature error, check the case temperatures - if the chiller or blower is not working then the case temperature is probably very high as well. If however the case temperature is within the normal range and the diode is over-temperature, then this means the TECs (thermo-electric Peltier coolers, that transfer heat from the laser diode to the case) are likely not working properly.
• If you get an error saying the temperature is too low to turn on laser, leave the device on for a few minutes.This should circulate enough coolant (or air) and warm things up enough for the laser to operate. A reset (or shutting the device off and back on) may be needed in some cases to clear the error off the head controller and allow the laser to turn on.