What is a thyristor regulator? It's a mechanism for control the power of a heater.

First, you don't need to remember the name "thyristor regulator." You can understand its role by looking at the temperature control flow.

Taking on the "operation side" of temperature control.

It's easier to understand if you think of it this way: the temperature controller determines "how much to heat," and the thyristor regulator translates that instruction into power for the heater.

For example, if the temperature controller sees the current temperature and determines that "more heating is needed," the thyristor regulator increases the power supplied to the heater in response to that operation.

Conversely, as the temperature approaches the set value, the power supplied to the heater is reduced in accordance with operation signal from the temperature controller.

In other words, a thyristor regulator is neither a device that measures temperature itself nor a device that performs PID computation to determine operation variable. It plays the role of adjusting the power actually supplied to the heater within the temperature control loop.

A thyristor is a semiconductor switch used in AC circuits.

A "semiconductor switch" is an electronic component that uses electrical signals to turn electricity on and off.

A thyristor has terminal called a "gate," and by passing a small current through it, the large current flowing to heaters and other components can be control.

Why is it easy to use for communication?

A thyristor has the property of remaining ON once it is switched ON until current flowing through it falls below a certain value.

In an AC signal, the polarity of current changes periodically, and there is a moment during this cycle when current becomes zero. A thyristor uses this characteristic of the AC signal to turn on and off control.

A thyristor regulator adjusts the power supplied from the AC power source to the heater by changing the timing of when the thyristor is turned ON.

In a thyristor regulator, instead of continuously supplying AC power to the heater, the power supplied to the heater is adjusted by changing the timing of the thyristor's operation.

Typical methods include "phase control" and "frequency division control."

Both systems use thyristors to regulate power, but they differ in "how they utilize the alternating current wave."

The alternating current voltage used in homes and factories is not constant, but changes periodically like a wave.

The concept of "where" this wave of alternating current is located is called "phase."

Phase control involves changing the timing of when the thyristor is turned ON in the AC wave.

If the ON timing is set earlier, the amount of time power is supplied to the heater within one cycle will be longer. If the ON timing is set later, the amount of power supplied to the heater can be reduced.

The timing of this ON state, expressed as an angle, is called the "control angle."

Characteristics of Phase control

Phase control allows for precise adjustment of the output because it enables the change of energization range within a single cycle of an AC current.

Furthermore, this method is easily compatible with heaters that have various electrical characteristic.

On the other hand, because it uses the AC wave from a certain point, the output waveform differs from the clean waveform of the power supply itself.

As a result, harmonics and high-frequency noise may be generated, potentially affecting surrounding power equipment and measuring instruments.

Frequency division control is a method that switches a thyristor ON/OFF at the moment the power supply voltage becomes zero.

Unlike phase control, which applies energization midway through an AC wave, this method uses the power supply cycle as a single unit and changes the ratio of the cycles that energization energization those that are not.

For example, the average power supplied to the heater will differ depending on whether you turn it ON for 4 out of 5 cycles and OFF for 1 cycle, or whether you turn it ON for only 1 out of 5 cycles.

While the device is ON, the power supply waveform is used without being cut off midway.

Characteristics of frequency division control

Compared to phase control, frequency division control is characterized by its ability to easily reduce high-frequency noise.

However, this does not mean that "no noise is generated with frequency division control." As long as electricity is being switched on and off, noise will be generated to varying degrees.

Furthermore, when the heater is turned on, the power supply voltage is directly applied to the heater, which may result in a large current flowing through heaters whose resistance changes significantly with temperature.

Depending on the conditions, it may also be necessary to consider the impact on the power supply, such as the flickering of lights.

In addition to thyristor regulators, SSRs (solid-state relays) are also used to electrically operation heaters.

What exactly is a relay?

A relay is a switch used to turn another electrical circuit ON or OFF using an electrical signal.

In a mechanical relay, electricity is turned on and off by physically moving the internal contact.

On the other hand, SSRs do not use mechanical contact; instead, they are electrically switched ON/OFF using semiconductors.

The SSR is ON/OFF, and the thyristor regulator adjusts the power.

SSRs are basically used as semiconductor switches that either allow electricity to flow or stop it.

In temperature control, one method involves repeatedly switching the SSR (Steam Sink Relay) on and off based on a signal from a temperature controller, thereby changing the proportion of time the heater is energization and adjusting heat quantity.

Thyristor regulators adjust the power supplied to the heater through methods such as phase control and frequency division control.

However, the relationship isn't simply that SSRs are a simplified version and thyristor regulators are high-order devices.

The appropriate control method, heater characteristic, and required power and current are selected accordingly.

When choosing a thyristor regulator, the electrical characteristic of the heater are particularly important.

Electric heaters convert electricity into heat by utilizing "electrical resistance," the property that makes it difficult for electricity to flow.

However, the extent to which that resistance value changes with temperature varies greatly depending on the type of heater.

In other words, even when the same voltage is applied, current flowing and the heat generated may vary depending on the type and temperature of the heater.

Nichrome-based and iron-chromium-based

Nichrome and iron-chromium heaters have characteristic of maintaining relatively resistance even when the temperature changes.

Such heaters can utilize voltage-based control, control without feedback, and frequency division control.

SiC type

SiC (silicon carbide) heaters have the characteristic that resistance resistance not only with temperature but also with usage time.

Therefore, even when the same voltage is applied, current flowing and heat quantity generated will change depending on the state of the heater.

In such cases, instead of just looking at the voltage, there is a method of control while checking the actual power being supplied to the heater.

Molybdenum silicide pure metal

In molybdenum disilicate and pure metal heaters, resistance value changes significantly with temperature.

Especially at low temperatures, resistance is low, so applying a large voltage directly can result in a large current flowing.

In this type of heater, a method is used to adjust the output while monitoring the actual current flowing.

This is where the word "feedback" comes in.

With thyristor regulators, there is a method of adjusting the output while checking the actual voltage output to the heater, current flowing, and the power being used.

This is a different feedback than PID control, which is performed by a temperature controller while monitoring the temperature.

Voltage feedback

We measure the actual voltage output to the heater and adjust the output of the thyristor regulator so that the voltage approaches the target voltage.

For example, even if the power supply voltage changes, you can correct it while checking the actual output voltage.

current feedback

current actually flowing to the heater is measured, and the output is adjusted based on that current.

To measure large current, a device called a CT (current converter) may be used.

In heaters where resistance changes significantly with temperature, a large current may flow at low temperatures.

In such cases, excessive current can be suppressed by adjusting the output while monitoring the actual current.

Power feedback

In power feedback, both voltage and current are measured.

Electricity can basically be thought of as "voltage × current".

We determine the actual power being supplied to the heater and adjust the output so that the power approaches the target.

In heaters with varying resistance, the required voltage and current combination changes even when supplying the same amount of power.

Therefore, there are methods of control that use power itself as the reference, not just voltage.

No feedback

There are also methods that do not check the actual voltage, current, and power inside the thyristor regulator, but instead adjust the output according to the input operation signal.

More feedback features aren't always better. The choice depends on the heater's characteristic and the required control method.

By observing how the heater's resistance changes with temperature and usage time, you can understand why feedback system is chosen.

When choosing a thyristor regulator, don't look at the model number first; instead, first check the heater and power supply requirements.

Thus, instead of "deciding on the thyristor regulator capacity first," it is important to consider the voltage, power, and current required for the heater, and then the electrical characteristic of the heater, in that order.

Thyristor regulators not only regulate power but also have the function of ensuring proper use of heaters and equipment.

The actual features included will vary depending on the model, but here are some typical concepts.

current limiting

This function limits the output to prevent current flowing to the heater from exceeding a set value.

resistance changes significantly with temperature, making it important in heaters and other devices where large current flow at low temperatures.

Soft Start

This function gradually increases the output at the start of operation, rather than suddenly increasing it all at once.

Heaters with low resistance at room temperature may experience a large current immediately after starting operation. This sudden current can be suppressed by gradually increasing the output.

It is also used to reduce the thermal stress on the heater caused by rapidly applying heat.

Heater disconnection alarm

Some models have a function that checks the status of the heater based on its voltage and current, and detects heater disconnection or abnormalities.

Detection methods and available conditions vary depending on the model.

When working with thyristor regulators for the first time, it's important to pay attention to measuring the output voltage and current.

In particular, with phase control, the output waveform is not a clean sine wave like a power supply, but a distorted waveform with parts of it cut off.

Therefore, general measuring instruments may not be able to display the correct voltage or current.

If you find that the voltage is lower than expected after taking measurements, don't immediately suspect a thyristor regulator malfunction. Instead, check what kind of waveform you are measuring and what kind of measuring instrument you are using.

A thyristor regulator is an important device that regulates the power supplied to a heater.

However, simply using a thyristor regulator does not guarantee stable temperature control.

Temperature control needs to be considered as part of the entire control loop, not just as a single device.

Various factors affect temperature control, including the measurement location of the temperature sensor, PID settings, heater capacity, thyristor regulator type, heat capacity of the control object, response delay, and external temperature changes.

Therefore, if there is a problem with temperature control, it is important to consider the cause from the entire control loop, rather than just suspecting the thyristor regulator.

CHINO offers thyristor regulators for use in combination with temperature controllers and other devices.

Depending on the product, the supported power supply voltage and current, single-phase/three-phase, phase control /frequency division control, feedback method, protection/alarm functions, etc., will vary.

This article aims to help you understand the mechanism of thyristor regulators and the considerations for selecting them, rather than providing detailed specifications for individual products.

When selecting a product, please check specifications of each product after confirming the requirements for the heaters and equipment you will be using.