I started with a ship full of max-level veterans, and I'm just a complete noob.

On Monday morning, the 502 technical team moved toolboxes, recorders, and spare parts into the No. 3 furnace room of the Institute of Physics.

Upon entering, Jiang Ming first unfolded the flowchart and posted it next to the stove rack, with a single line of text written at the top:

"No one should touch the heating circuit before the furnace is actually running."

Huang Kun reviewed the entire document from beginning to end, and then signaled to the duty officer to hand over the original records and equipment keys.

The quartz tube of Furnace No. 3 is horizontally mounted in the refractory brick trough, and the flanges at both ends are sealed with old-style pressure caps. The induction coil is connected to the feed screw, and the burn marks left from previous tests are still attached to the inside of the furnace wall.

Old Sun walked around the furnace frame, first gripping the pusher handwheel and turning it. When the screw rod was turned to the fixed position, the copper nut would move axially, and the graduations on the reading dial would also shift accordingly.

"This thing wobbles as it moves, so even if the temperature is stable, it can't maintain the molten zone."

He disassembled the transmission box, took out the worn copper nut, measured three dimensions with a micrometer, and then drew a split nut with a preload spring on the back of the drawing.

Da Liu moved the temporary worktable to the side of the furnace frame, welded the Wheatstone bridge and two-stage DC amplifier, arranged the power lines and measuring lines in separate slots, and unified the grounding point at one end of the frame.

Fang Xudong sat in front of the recorder, adjusted the time reference of the pyrometer, the double platinum resistance bridge and the heating ammeter to the same position, and then used a stopwatch to check the paper feed speed.

Jiang Ming installed two platinum resistance thermometers into a ceramic protective sleeve, one near the front edge of the predetermined melting zone and the other at the rear edge, with the distance between the two locations re-determined according to the width of the melting zone provided by physics.

Lin Lanying stood beside him with the old furnace temperature record. Seeing him repeatedly adjusting the sensor position, she handed him the hot zone distribution map she had drawn when the furnace was dismantled last year.

"The temperature is highest in the center of the coil, and the actual melting zone will be biased towards the direction of propulsion. If you place it according to the geometric center, the differential signal will be inherently biased."

Jiang Ming took the blueprints, moved the front sensor outward by one grid, and then asked Fang Xudong to mark the correction distance on the recording paper.

"First, locate the old hot zone, then raise it to 700 degrees Celsius, and then use a pyrometer to check the temperature difference between the two ends."

When Huang Kun came over from the office, Lao Sun had already removed the lead screw and was using a fine file to repair the newly machined copper nut. On the workbench were two preloaded springs that were only half-assembled.

He leaned down to look at it and asked, "If we're doing no-load temperature control today, does the transmission mechanism also need to be modified?"

Old Sun swept the copper shavings into the iron box, running his finger along the polished edge of the screw thread.

"Temperature records and propulsion speed must be recorded on the same piece of paper. If we skip this step today, we'll have to disassemble it again when loading materials."

Huang Kun turned to Jiang Ming, who was measuring the zero point of the bridge. The galvanometer spot was stopped in the center of the scale, and after the power was switched, it only moved one small division to the right.

"The two-stage amplifier needs to be warmed up for forty minutes, the zero-point drift needs to be reduced to the allowable range, and the actuator needs to complete three full strokes on its own."

Jiang Ming pushed the pressure regulator handle to the starting position, and Da Liu activated the electromagnetic actuator. The iron core drove the connecting rod forward, rotated through the set angle, and then returned to its original position.

The first return trip left a two-mark deviation. Old Sun disassembled the connecting rod pin and added a thin copper sleeve inside the hole. The second deviation was reduced to half a mark, and the third time it had fallen back to the original mark.

Around 11 a.m., all the circuits passed the insulation test, and the double platinum resistance thermometers were calibrated at three points using the standard furnace of the Institute of Physics. The correction values ​​were written into the table next to the bridge one by one.

Jiang Ming adjusted the three sets of knobs for proportional, integral, and differential functions to their initial positions. These parameters were derived from the heating curves in the old records of Furnace No. 3, and also incorporated the actuator response of Furnace No. 502.

Fang Xudong pressed the recorder switch, and the three pen tips drew straight ink lines on the paper tape. Huang Kun stood on the other side of the recording table, holding a hardcover notebook in his hand.

"power ups."

Da Liu turned on the main switch, the heating coil emitted a low hum, the ammeter pointer crossed the first red line, and then stopped at the predetermined position.

Before the furnace temperature rises to 400 degrees Celsius, the automatic circuit only undertakes minor corrections, the actuator operates smoothly, and the differential value of the dual platinum resistance thermometer remains within a narrow range.

After exceeding 600 degrees Celsius, the inner wall of the quartz tube began to shine, and the leading edge of the temperature measuring line first rose upwards, while the trailing edge of the curve followed at a distance.

Jiang Ming turned the differential compensation knob back two notches, causing the controller to reduce the heating current. The furnace temperature curve slowed down, but still rose along the set slope.

Lin Lanying bent down to examine the record sheet, her fingertip hovering at a 780-degree angle.

"The temperature difference between the front and rear edges is 1.6 degrees Celsius greater than that of the old furnace, which may indicate that the coil's hot zone is misaligned."

"Write it down first, then check it again at 850 degrees."

Fang Xudong used a red pencil to mark the temperature difference changes, and at the same time wrote the moment of each actuator action on the edge of the paper tape, and the records gradually formed a set of staggered peaks and valleys.

At 850 degrees, the reading of the pyrometer differed from the value converted by the bridge by 0.7 degrees. Jiang Ming corrected the absolute temperature according to the calibration curve, and the differential control continued to operate according to the original signal.

As the furnace temperature continued to approach 900 degrees Celsius, the voltage regulator began to operate frequently, and each time the ammeter needle dropped, the temperature curve would still climb upwards for a while.

"The thermal inertia is greater than recorded."

Fang Xudong circled the delay between the two actions. The old record showed it to be more than seven minutes, but the curve in front of him had already dragged on for more than ten minutes.

Jiang Ming watched as the paper tape was ejected, then pressed his palm against the edge of the control panel, temporarily preserving the original parameters to allow the complete response to continue to appear.

At 912 degrees, the proportional element exceeds the set response for the first time, and the actuator reduces the current, but the integral term continues to accumulate the previous error.

The temperature climbed to 921 degrees before starting to drop. After falling below 916 degrees, the actuator increased the heating current again, and the recovery speed was faster than before.

The curves on the paper tape changed from gentle ripples to wide undulations, with the peak and trough values ​​separated by six degrees, and the amplitude of the second round of oscillations expanded to nine degrees.

Da Liu stood guard by the main switch, his eyes following the ammeter as it moved back and forth. Lao Sun put down the copper nut in his hand and went to the back of the furnace to check the quartz tube support.

"The support hasn't been moved, and the tubing is stable; the problem is in the circuit."

When the temperature rose above 925 degrees Celsius in the third round, Jiang Ming turned the integration knob back. The accumulated error continued to push the actuator in the old direction, and the furnace temperature continued to rise.

Fang Xudong reported the data: "927.4, the leading edge is still rising, and the trailing edge is delayed by 12 minutes and 20 seconds."

Jiang Ming reached out and switched to manual control, pressing the pressure regulator back to a safe position. The furnace temperature started to drop around 928 degrees Celsius, but the curve left a high and wide peak.

The only sound in the laboratory was the friction of the recorder moving the paper. Huang Kun had been standing in the same spot since the power was turned on, and only now did he lower his head and open the hardcover record book.

He wrote down the peak value, period, and actuator angle at the corresponding position of 920 degrees, and then drew a question mark in the last column.

Lin Lanying laid out the curve of the No. 3 furnace from the previous year next to her. The two records showed similar heating trends before reaching 800 degrees Celsius, but diverged into completely different trajectories after entering the high-temperature zone.

"The old system used manual pressure regulation. If the operator found that the temperature was rising too fast, they would take it back in advance. The automatic circuit was already slowing down due to the error."

Jiang Ming copied the peak and valley data from earlier onto the flowchart, listing proportional response, integral accumulation, and actuator hysteresis separately.

Huang Kun closed the notebook and looked at the three sets of knobs on the control panel.

"The parameters you provided cause the furnace temperature to oscillate continuously around 920 degrees Celsius. At this rate, it won't even be able to get within plus or minus 0.5 degrees Celsius."

Wu Hanzhang stood by the door, put the half-smoked cigarette back into the cigarette pack, and waited for Jiang Ming's reply.

Jiang Ming abandoned his attempt to explain, pulled out the paper tape that Fang Xudong had just replaced, and superimposed the three peak values ​​and valley values ​​on the old record. The difference in delay was now clearly visible on the scale.

"This set of parameters is invalid."

Huang Kun pressed his pencil against the cover of the notebook, still waiting for the next sentence.

Jiang Ming raised his hand and pointed to the heating circuit of Furnace No. 3, his gaze moving along the quartz tube, sensor and actuator one by one.

"Remeasure the time constant for me."