Coolant and airflow¶
This page describes the machine's thermal hardware: the coolant loop, the airflow path, and the controls and readbacks each piece offers. How ForgeFIRM's cooling engine drives them is on the cooling engine; what the operator sees and can set is on Cooling and fans.
The tube is water-cooled and the enclosure is air-cleared, and both matter while the laser fires: coolant that has stopped circulating will let a tube overheat within a cut, and smoke that is not pulled out spoils the work and fogs the optics.
The coolant loop¶
The coolant loop is closed: a pump, a radiator with fans, the laser tube, and two thermistors, one upstream of the tube and one downstream of a small inline heater. Pro machines are specified with a thermoelectric cooler (TEC) on the loop; the board cannot tell whether one is fitted, because the TEC output has no readback. The heater exists for diagnostics, not for warming the machine up: it is how the cooling engine proves the coolant is actually moving (see the cooling engine).
| Piece | Control | Notes |
|---|---|---|
| Pump | thermal/water_pump_on (0 = off, 1 = on) |
A pump stop/start cycle can airlock the loop. |
| Inline heater | thermal/heater_pwm (0 to 65535, 0 = off) |
Sits in the loop between the two water temperature sensors, so heat it puts in shows up as a difference between them. |
| TEC | thermal/tec_on (0 = off, 1 = on) |
Pro machines only. Basic and Plus have no TEC fitted, and writing here does nothing on those. |
| Upstream thermistor | pic/water_temp_2 |
10 kΩ B3380 NTC; conversion on Sensors. |
| Downstream thermistor | pic/water_temp_1 |
Same sensor, downstream of the heater. |
| TEC temperature | pic/tec_temp |
Pro only; conversion unknown; rails at 1023 without a TEC. |
Coolant temperature is read, not guessed. Both thermistors are converted with the factory's own beta-equation curve, checked against a thermometer (Sensors). A sensor reading at either rail is treated as open or shorted, not as a temperature.
The airflow path¶
The airflow path has four independently driven pieces:
| Piece | What it does | Control |
|---|---|---|
| Exhaust blower | pulls smoke out of the enclosure | thermal/exhaust_pwm (0 to 65535) |
| Two intake fans | feed clean air in behind it | thermal/intake_pwm (0 to 65535); one output drives both fans |
| Air assist (in the head) | blows the cut line clear at the focal point | head/air_assist_pwm (0 to 1023); the factory firmware never sets it below 204, so the fan is never off |
| Purge air (in the head) | keeps the optics clean by purging smoke from the lens cavity; on whenever the machine is on | head/purge_air (0 = off, 1 = on) |
Every fan reports a tachometer, so the engine can tell a commanded duty from an
actual airflow, and the panel shows real speeds rather than setpoints: the
exhaust (thermal/tach_exhaust), each intake (thermal/tach_intake_1,
thermal/tach_intake_2) and the air assist (head/air_assist_tach) report
the period between tach pulses. The purge-air fan has no tachometer and
reports its current instead (head/purge_air_current). The period units and
RPM formulas are on Sensors.
What the fans actually reach¶
Measured on the bench reference (The bench reference) at the cut profile, sampled once a second for two minutes from idle:
| Fan | Steady | Spread | Time to 90 % | At idle |
|---|---|---|---|---|
| Exhaust | 11640 rpm | 11444 to 11947 | 5 s | 0 rpm (off) |
| Intake 1 | 4157 rpm | under 100 rpm | 7 s | about 745 rpm |
| Intake 2 | 4158 rpm | under 100 rpm | 7 s | about 745 rpm |
| Air assist | 11050 rpm | 30 rpm | 1 s | about 1900 rpm (duty 204) |
| Purge air | about 625 counts of current | about 625 (always on) |
The purge fan reads about 1 with no current at all, which is what a dead one looks like.
These are the numbers ForgeFIRM's airflow floors ship at 55 percent of, and the spin-up times are why the gates have a grace window (the cooling engine). They are one machine's: an exhaust duct with an inline booster fan changes the back pressure and can move the exhaust reading by a few percent either way, and the commissioning airflow check measures your machine's own (Commissioning).
What the kernel does on its own¶
On a dead man's switch trip, and on module removal, the kernel de-energizes the heat sources only, the loop heater and the TEC, and touches nothing else. The pump, the exhaust and intake fans and the head airflow belong to the cooling engine and stay as they are, deliberately: see the kernel module for why.
The attribute reference for every control above is on the kernel module.