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

After midnight, Jiang Ming drew the curtains back tight and bolted the door. The teacup on the table still bore the water stains from the daytime.

He first communicated with his third fellow disciple.

The experimental setup unfolded deep within his consciousness, with dual thermocouples, a differential amplifier, and a power actuator arranged in sequence. His third classmate drew two temperature measurement lines on the blackboard with chalk, one at the leading edge and one at the trailing edge, and finally connected the two lines to the amplifier input.

"When the temperature drifts in the same direction, the differential will cut off a portion of it."

Jiang Ming asked, "How do you ensure accuracy in the high-temperature range?"

The third student broke the chalk in two.

"Calibrate first, then enlarge; don't treat instruments like divine pronouncements."

"The melting zone is close to 937 degrees Celsius, and the requirement is plus or minus 0.1 degrees Celsius."

The third student looked at the numbers on the blackboard, picked up a screwdriver, and tapped it twice on the table.

"I make measuring instruments. You have to measure the thermal inertia of the metallurgical furnace, the width of the melting zone, and the heat dissipation of the quartz tube yourself."

"Can differential compensation be used?"

"It works; the basic structure works."

He marked out a blank area on the connecting line between the two thermocouples.

"But what you need is a high-temperature servo motor, not just stable readings. Go find my teacher."

The light behind the experimental table dimmed, and the figure of the third fellow student retreated into the depths of the book pages.

Jiang Ming turned to the newly appeared gray humanoid figure.

A bald, middle-aged man stood beside three platinum resistance thermometers with different ranges. Round-framed pince-nez glasses hung on the bridge of his nose. Behind the lenses, his eyes first looked at the thermometers, then at the germanium rod sketch in Jiang Ming's hand.

"Regional purification?"

He pronounced the unfamiliar word with a heavy Bavarian accent.

"I don't recognize the term, but the temperature control you're talking about is the same kind of problem I encountered with the quartz crystal temperature baths I made for Siemens."

Jiang Ming explained the melting zone, propulsion mechanism, and temperature curve, compressing the requirements into three aspects: temperature measurement error, control cycle, and thermal inertia.

Kruger picked up a platinum resistance thermometer and looked at the scale under the light.

"Thermocouples have strong signals, but their reproducibility and linearity at high temperatures are insufficient. Platinum resistance thermometers have weak signals, but they can break down temperature changes into finer details."

He drew the Wheatstone bridge on paper.

"Use two platinum resistance thermometers, one before and one after the melting zone, and measure the difference between them using a bridge circuit. The output is then amplified by two stages of DC and sent to the power actuator."

Jiang Ming pressed further: "When the melting zone approaches 1,000 degrees Celsius, the temperature coefficient of the platinum resistance thermometer will change."

"Therefore, it needs to be revised."

Kruger placed the three thermometers side by side back on the table.

"When high-temperature materials enter another working range, temperature and resistance are no longer suitable to be expressed by a straight line. Quadratic compensation is used. First, the curve is fitted by the calibration point, and then the compensation curve is connected to the comparison stage."

Jiang Ming picked up the chalk and wrote the temperature function on the blackboard.

Kruger glanced at it and took out a lab notebook with its corners curled up.

"You need to measure the furnace's time constant first."

"How do you measure it?"

"Give the heating power a step change and record the time it takes for the molten zone temperature to go from the initial value to the stable value. Don't rush to speed up the loop. The thermal inertia is not yet clear. If the servo bandwidth is too high, the furnace temperature will fluctuate back and forth."

He wrote down the terms proportional, integral, and differential next to the step curve.

"If the ratio is too small, the response is slow; if the ratio is too large, the temperature fluctuates. Integral is responsible for eliminating long-term deviations, while differential is used to observe the trend of change and can amplify every measurement fluctuation in high-temperature noise."

How are the parameters determined?

Kruger flipped to the 1934 record, his finger moving along the step response curve.

"First, remove the integral and derivative, gradually increase the ratio until the system exhibits sustained constant-amplitude oscillations, and then calculate the three parameters based on the critical gain and oscillation period."

He listed several sets of experience relationships and added applicable conditions next to them.

"This is just the initial value. The quartz tube, atmosphere, and germanium rod mass of the furnace will all change the time constant. The final parameters need to be corrected by the physical step response."

Jiang Ming memorized all the formulas.

"If the load is changed from an empty tube to a germanium rod, will the parameters need to be readjusted?"

"certainly."

Kruger lifted his glasses and his gaze fell on Jiang Ming's face.

"What you need to control is the melting zone. The furnace only provides heat. When the load changes, the response changes. The no-load curve can only serve as the first line of defense."

This statement coincides with the records Jiang Ming saw in physics.

The fluctuation of ±3 degrees comes from open-loop control, while the ±0 degree requires the joint work of measurement, model and actuator. If any one of them deviates, the whole loop will send the error back to the melting zone.

As the psychic session drew to a close, Kruger handed him the last page of the record.

"Incorporate the high-temperature nonlinearity of platinum resistance thermometers into the compensation; don't just extrapolate it directly from the low-temperature calibration table."

"I will measure the time constant first, and then do the tuning."

"Very good, the stove will tell you what it is, you just need to listen carefully."

The figures of the lab bench, thermometer, and Kruger gradually faded away, and Jiang Ming withdrew from the depths of his consciousness.

The water ripples on the teacup on the table were still there, and the flame of the lamp wick maintained its original shape; less than two seconds had passed in the outside world.

He spread out the graph paper, first writing down the differential temperature measurement of the double platinum resistance thermometer, then the Wheatstone bridge, two-stage DC amplification, and electromagnetic actuator voltage regulation, and finally listing the PID parameter tuning and high-temperature nonlinearity correction on the right.

The technical sources of the solution need to be verifiable.

Qian Xuesen’s lecture notes contain the basics of automatic control, Ivanov’s personal notes mention Soviet-made constant-temperature resistance furnaces, and 502 has accumulated experience in high-temperature amplification and power supply stability on the Yuanlei No. 1 exhaust furnace. These three clues, when put together, are enough to support a cross-disciplinary derivation.

However, if Fang Xudong were to question every single parameter of the formula, the explanation would become weak.

Jiang Ming suppressed his doubts at the bottom of the page and began drawing the circuit diagram.

The first image shows a dual platinum resistance temperature measurement structure, with two sensors located near the leading and trailing edges of the molten zone, respectively, and outputting differential voltages via a bridge circuit.

The second diagram shows a two-stage DC amplifier with added shielding and zero-point adjustment at the input, and voltage regulation and reverse protection added to the power supply section.

The third diagram shows the power execution circuit. The electromagnet drives the voltage regulating mechanism, and the proportional, integral, and differential signals enter the comparison node respectively. The heating current is then controlled by the total error signal.

He then wrote the test order next to the three images.

First, measure the no-load time constant, then measure the time constant after the quartz tube is loaded, then load the germanium rod, and finally recalibrate the parameters based on the moving speed of the molten zone.

As night crept through the gaps in the curtains, the twelve-page proposal had already filled the worktable.

Jiang Ming flattened the last page, turned to the title page, and noted the technical recommendations for the temperature control system of the regional purification furnace at the Institute of Physics, Chinese Academy of Sciences, in the upper right corner.

Footsteps came from outside the cubicle, and the door lock was turned with a key.

Wu Hanzhang pushed open the door and came in, carrying a canvas bag. He glanced at the table, picked up the first page, and then turned to the second page.

Upon seeing the double platinum resistance structure, he pressed the paper down slightly.

When he saw the bridge sensitivity calculation, he took off his glasses and wiped them.

When he turned to the page on PID parameter tuning, his eyebrows were already furrowed.

Where did you learn PID tuning?

Jiang Ming pointed to the black lecture notes in the corner of the workbench.

"The last two pages of Mr. Qian's chapter on automatic control have an entry point, and I also checked the English journal index in the factory's archives."

Wu Hanzhang walked over, opened the lecture notes, and found the half-page of text about engineering simplification.

He stared at the formula for thirty seconds, then turned back to flip through the twelve-page proposal.

"Half a page can grow into twelve pages?"

"The entrance can indicate the direction, but the actual items still need to be made by ourselves."

Wu Hanzhang closed the lecture notes, picked up three circuit diagrams, rolled them up, and stuffed them into his canvas bag.

"Let's go to the Institute of Physics and let Huang Kun see for himself."

Around 6 a.m., the door to Laboratory 502 was locked again.

Jiang Ming walked out of the factory area with the proposal. In his canvas bag, besides twelve pages of manuscript paper, there were also sample specifications for a double platinum resistance thermometer, an old pyrometer, and a pressure regulating actuator removed from the exhaust furnace.

The first answer sheet has been submitted within the three-day deadline.

Next, Huang Kun will first look at the formula on the paper before deciding whether to hand over the germanium material to 502.