Impulse current generating device

Abstract

The utility model provides an impact current generating device, including control unit, direct current booster unit, impact current generating unit and communication unit, impact current generating unit includes short -circuit calibration loop, first take load calibration loop and second take load calibration loop, and control unit is connected with remote man -machine interaction unit communication through communication unit. The utility model provides an impact current generating device, can produce 6.4 / 69 mu s impact current waveform, can be used for indirect thunderbolt electricity test between helicopter, satisfies SAEAEP5412A, SAEAEP5416A, RTCA / DO-160G S22 etc. Military standard test requirement, can realize the waveform parameter calibration under different load conditions, realizes the remote operation of test process through communication module and remote man -machine interaction unit communication, has good man -machine interaction ability, fully guarantees the personal safety of operating personnel.

Description

Technical Field

[0001] This utility model relates to the field of electromagnetic compatibility immunity testing technology, and in particular to an impulse current generating device. Background Technology

[0002] Impulse current generators are widely used for performance testing of surge protective devices (SPDs) against indirect and direct effects of lightning or other transient overvoltages. Traditional impulse current generators are generally used for testing in civilian and industrial fields, and the tested devices are usually passive surge protection devices and power supply protection modules. The pulse waveforms of impulse current generators are mostly 8 / 20μs, and the output energy is usually small, lacking strong load-carrying capacity. The calibration method is output port short-circuit calibration, which does not have the ability to calibrate waveform parameters under load. The control unit and high-voltage pulse forming unit are integrated into one design, without sufficient safety protection distance, resulting in insufficient safety protection for operators. Utility Model Content

[0003] The purpose of this invention is to provide an impulse current generating device that can solve one or more of the problems in the prior art mentioned above.

[0004] According to one aspect of the present invention, an inrush current generating device is provided, comprising a control unit, a DC boost unit, an inrush current generating unit, a communication unit, and an indicator light. The control unit is electrically connected to the DC boost unit and can control the DC boost unit to output DC voltage. The inrush current generating unit includes a short-circuit calibration circuit, a first on-load calibration circuit, and a second on-load calibration circuit. The control unit can switch between the short-circuit calibration circuit, the first on-load calibration circuit, and the second on-load calibration circuit. The output terminal of the DC boost unit is connected to the input terminal of the inrush current generating unit. The output terminal of the inrush current generating unit is connected to a short-circuit test lead or a load under test. The control unit is communicatively connected to a remote human-machine interface unit through the communication unit. The indicator light is electrically connected to the control unit.

[0005] In some embodiments, the inrush current generating unit includes a resistor R1, a capacitor C1, a capacitor C2, a switch K1, an ignition gap switch G, a switch K2, a resistor R2, an inductor L1, a switch K3, a resistor R3, a resistor R4, an inductor L2, and a switch K4. The positive terminal of the inrush current generating unit's input is connected to one end of the ignition gap switch G through the resistor R1. The end of the ignition gap switch G connected to R1 is connected to the negative terminal of the inrush current generating unit's input through capacitors C1 and C2 connected in parallel. Switch K1 is connected in series with capacitor C2. A first branch and a second branch are connected in parallel between the other end of the ignition gap switch G and the positive terminal of the inrush current generating unit's output. The first branch includes a switch K2, a resistor R2, and an inductor L1 connected in series. The second branch includes a switch K3, a resistor R3, a resistor R4, and an inductor L2 connected in series. Switch K4 is connected in parallel across the two ends of the resistor R4. The negative terminal of the inrush current generating unit's input is connected to the negative terminal of the inrush current generating unit's output.

[0006] In some implementations, the short-circuit calibration circuit includes resistor R1, capacitor C1, capacitor C2, ignition gap switch G, switch K2, resistor R2, and inductor L1; the first load calibration circuit includes resistor R1, capacitor C1, ignition gap switch G, switch K3, resistor R3, resistor R4, and inductor L2; the second load calibration circuit includes resistor R1, capacitor C1, ignition gap switch G, switch K3, resistor R3, and inductor L2.

[0007] In some implementations, the DC boost unit includes a pulse width control circuit, a push-pull inverter circuit, a DC voltage multiplier circuit, and a resistor voltage divider sampling circuit. The input terminal of the pulse width control circuit is electrically connected to the control unit, and the output terminal of the pulse width control circuit is connected to the input terminal of the push-pull inverter circuit. The output terminal of the push-pull inverter circuit is connected to the primary side of the transformer in the DC voltage multiplier circuit, and the primary side of the transformer is connected to a DC voltage. The output terminal of the DC voltage multiplier circuit serves as the output terminal of the DC boost unit and is connected to the input terminal of the inrush current generating unit. The output terminal of the DC voltage multiplier circuit is connected to the input terminal of the resistor voltage divider sampling circuit, and the output terminal of the resistor voltage divider sampling circuit is connected to the signal input terminal of the control unit.

[0008] In some implementations, the pulse width control circuit includes a PWM control chip U2; the push-pull inverter circuit includes field-effect transistors Q1 and Q2, the output terminal of the PWM control chip U2 is connected to the gates of field-effect transistors Q1 and Q2 respectively, and the PWM control chip U2 can control the conduction and cutoff of field-effect transistors Q1 and Q2; the DC voltage multiplier circuit includes a transformer T3, the primary side of which is connected to a DC voltage, and the PWM control chip U2 can control the conduction and cutoff of field-effect transistors Q1 and Q2 to invert the DC voltage on the primary side of the transformer T3 into a DC pulse voltage, and the transformer T3 boosts the DC pulse voltage once. The DC voltage multiplier circuit also includes a secondary boost module, which includes several capacitors and several diodes disposed on the secondary side of the transformer T3, and the secondary boost module boosts the voltage on the secondary side of the transformer T3 a second time and outputs it as the output voltage of the DC boost unit to the inrush current generating unit.

[0009] In some implementations, the impulse current generating unit is capable of generating a 6.4 / 69μs impulse current waveform.

[0010] In some implementations, the remote human-machine interface unit is an industrial panel PC, which is connected to the communication unit via optical fiber.

[0011] In some implementations, an LCD touchscreen is also included, which is electrically connected to the control unit.

[0012] The impulse current generator provided by this utility model can generate a 6.4 / 69μs impulse current waveform, which can be used for helicopter indirect lightning testing and meets the military standard testing requirements such as SAEARP5412A, SAEARP5416A, and RTCA / DO-160G S22. It can achieve parameter calibration of 6.4 / 69μs indirect lightning waveform under different load conditions. It can communicate with a remote human-machine interaction unit through a communication module to realize remote operation of the test process, has good human-machine interaction capabilities, and fully protects the personal safety of operators.

[0013] In addition, unless otherwise specified, all aspects of this utility model technical solution can be implemented by conventional means in the field. Attached Figure Description

[0014] To more clearly illustrate the technical solutions of the embodiments of this utility model, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 This is a schematic diagram of the structure of an impulse current generating device provided in an embodiment of the present invention.

[0016] Figure 2 The circuit diagram of the impulse current generating unit in the impulse current generating device provided in an embodiment of the present invention.

[0017] Figure 3 The circuit diagram of the DC boost unit in the impulse current generating device provided in one embodiment of this utility model. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of this utility model clearer, the technical solutions of the embodiments of this utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this utility model, not all embodiments. Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this utility model.

[0019] Example: In this embodiment, please refer to the appendix to the specification. Figure 1-3 It provides an inrush current generating device, including a control unit 1, a DC boost unit 2, an inrush current generating unit 3, and a communication unit 4.

[0020] The control unit 1 is electrically connected to the DC boost unit 2, and the control unit 1 can control the DC boost unit 2 to output DC voltage. The control unit 1 is also electrically connected to the inrush current generating unit 3, which includes a short-circuit calibration circuit, a first on-load calibration circuit, and a second on-load calibration circuit. The control unit 1 can switch between the short-circuit calibration circuit, the first on-load calibration circuit, and the second on-load calibration circuit. The output terminal of the DC boost unit 2 is connected to the input terminal of the inrush current generating unit 3, and the output terminal of the inrush current generating unit 3 is connected to the short-circuit test lead or the load under test. The control unit 1 is connected to the remote human-machine interaction unit 5 through the communication unit 4.

[0021] Control unit 1 can use STM32F427ZGT6 microcontroller. Control unit 1 can control the DC boost unit 2 to output DC voltage, and can also control the inrush current generating unit 3 to generate inrush current.

[0022] The inrush current generating unit 3 may include resistor R1, capacitor C1, capacitor C2, switch K1, ignition gap switch G, switch K2, resistor R2, inductor L1, switch K3, resistor R3, resistor R4, inductor L2 and switch K4.

[0023] The positive terminal of the input of the impact current generating unit 3 is connected to one end of the ignition gap switch G through resistor R1. The end of the ignition gap switch G connected to R1 is connected to the negative terminal of the input of the impact current generating unit 3 through capacitors C1 and C2 connected in parallel. Switch K1 is connected in series with capacitor C2. The other end of the ignition gap switch G and the positive terminal of the output of the impact current generating unit 3 are provided with a first branch and a second branch connected in parallel. The first branch includes a switch K2, a resistor R2 and an inductor L1 connected in series. The second branch includes a switch K3, a resistor R3, a resistor R4 and an inductor L2 connected in series. Switch K4 is connected in parallel across resistor R4. The negative terminal of the input of the impact current generating unit 3 is connected to the negative terminal of the output of the impact current generating unit 3.

[0024] The short-circuit calibration circuit includes resistor R1, capacitor C1, capacitor C2, ignition gap switch G, switch K2, resistor R2, and inductor L1; the first load calibration circuit includes resistor R1, capacitor C1, ignition gap switch G, switch K3, resistor R3, resistor R4, and inductor L2; the second load calibration circuit includes resistor R1, capacitor C1, ignition gap switch G, switch K3, resistor R3, and inductor L2.

[0025] Depending on the different testing requirements, the control unit 1 controls the opening and closing states of each switch in the impulse current generating unit 3 to generate and calibrate the impulse current.

[0026] Specifically, when a short-circuit calibration test is required at the output port of the impulse current generator, the output port of the impulse current generator is connected through a short-circuit test lead. Control unit 1 controls switches K1 and K2 to close, and switches K3 and K4 to open. At this time, the DC voltage output by DC boost unit 2 charges capacitors C1 and C2 through resistor R1. When the charging voltage reaches the expected value, the ignition gap switch G is triggered and turned on. Capacitors C1 and C2, switch K2, resistor R2, inductor L1 and short-circuit test lead form a discharge circuit, generating a 6.4 / 69μs impulse current waveform.

[0027] When a 20uH helicopter load calibration test is required, the output port of the inrush current generator is connected to the helicopter load. Control unit 1 controls switches K1 and K2 to open, switch K3 to close, and switch K4 to open. At this time, the DC voltage output by DC boost unit 2 charges capacitor C1 through resistor R1. When the charging voltage reaches the expected value, the ignition gap switch G is triggered and turned on. Capacitor C1, switch K3, resistor R3, resistor R4, inductor L2 and helicopter load form a discharge circuit, generating a 6.4 / 69μs inrush current waveform.

[0028] When a 20uH series 5Ω helicopter load calibration test is required, the output port of the inrush current generator is connected to the helicopter load. Control unit 1 controls switches K1 and K2 to open and switches K3 and K4 to close. At this time, the DC voltage output by DC boost unit 2 charges capacitor C1 through resistor R1. When the charging voltage reaches the expected value, the ignition gap switch G is triggered and turned on. Capacitor C1, switch K3, resistor R3, inductor L2 and helicopter load form a discharge circuit, generating a 6.4 / 69μs inrush current waveform.

[0029] Therefore, the impulse current generating device provided by this utility model can perform parameter calibration under different load conditions, and realize short-circuit calibration test, 20uH helicopter load calibration test and 20uH series 5Ω helicopter load calibration test.

[0030] In an optional embodiment, the DC boost unit 2 may include a pulse width control circuit, a push-pull inverter circuit, a DC voltage multiplier circuit, and a resistor voltage divider sampling circuit. The input terminal of the pulse width control circuit is electrically connected to the control unit 1, and the output terminal of the pulse width control circuit is connected to the input terminal of the push-pull inverter circuit. The output terminal of the push-pull inverter circuit is connected to the primary side of the transformer in the DC voltage multiplier circuit, and the primary side of the transformer is connected to a DC voltage. The output terminal of the DC voltage multiplier circuit serves as the output terminal of the DC boost unit 2 and is connected to the input terminal of the inrush current generating unit 3. The output terminal of the DC voltage multiplier circuit is connected to the input terminal of the resistor voltage divider sampling circuit, and the output terminal of the resistor voltage divider sampling circuit is connected to the signal input terminal of the control unit 1.

[0031] The pulse width control circuit includes a PWM control chip U2; the push-pull inverter circuit includes field-effect transistors Q1 and Q2. The output of the PWM control chip U2 is connected to the gates of field-effect transistors Q1 and Q2, respectively. The PWM control chip U2 can control the conduction and cutoff of field-effect transistors Q1 and Q2. The DC voltage multiplier circuit includes a transformer T3. A DC voltage is connected to the primary side of transformer T3. The PWM control chip U2 can control the conduction and cutoff of field-effect transistors Q1 and Q2 to invert the DC voltage on the primary side of transformer T3 into a DC pulse voltage. Transformer T3 boosts the DC pulse voltage once. The DC voltage multiplier circuit also includes a secondary boost module, which includes several capacitors and several diodes disposed on the secondary side of transformer T3. The secondary boost module boosts the voltage on the secondary side of transformer T3 a second time and outputs it as the output voltage of DC boost unit 2 to the inrush current generating unit 3.

[0032] The PWM control chip U2 can be an SG3525A PWM control chip. The input terminal of PWM control chip U2 is connected to the signal output terminal of control unit 1. Control unit 1 outputs control signals to PWM control chip U2, and PWM control chip U2 can output PWM drive signals under the control of control unit 1. PWM control chip U2 can generate two 5V, 50kHz frequency, 40mA maximum output current, dynamically adjustable PWM drive signals. The output terminal of PWM control chip U2 is connected to the gates of MOSFETs Q1 and Q2 in the push-pull inverter circuit, thereby controlling the conduction and cutoff of MOSFETs Q1 and Q2.

[0033] A resistor R5 is placed between the gate of MOSFET Q1 and the output terminal of PWM control chip U2, and a resistor R6 is placed between the gate of MOSFET Q2 and the output terminal of PWM control chip U2. Resistors R5 and R6 are gate current-limiting resistors for the MOSFETs and can be 10Ω. The gate of MOSFET Q1 is grounded through resistor R7, and the gate of MOSFET Q2 is grounded through resistor R8. Resistors R7 and R8 are gate voltage-limiting resistors for the MOSFETs, protecting their gates. MOSFETs Q1 and Q2 are N-channel enhancement-mode MOSFETs. Resistor R11 and capacitor C7 form an RC snubber circuit to absorb the reverse electromotive force of transformer T3, preventing excessive reverse voltage from causing MOSFETs Q1 and Q2 to break down. Transformer T3 is a high-frequency pulse boost transformer, wound with an E-type manganese-zinc ferrite core. The primary winding has N1 = 30 turns, and the secondary winding has N2 = 1500 turns, with a turns ratio of N2 / N1 = 1500 / 30 = 50, enabling DC boost functionality. Capacitors C3, C4, C5, and C6 are high-voltage ceramic capacitors with a value of 1nF. Together with diodes D4, D5, D6, and D7, they form a DC 4x voltage multiplier shaping circuit, enabling secondary boost functionality. Resistors R12, R13, R9, and R10 form a DC voltage divider circuit with a voltage division ratio of 1000:1. R12 and R13 are high-voltage resistors, serving as the high-voltage arm of the voltage divider circuit, while R9 and R10 are metal film resistors, serving as the low-voltage arm. A and B are connected to the signal input terminals of control unit 1.

[0034] Therefore, the PWM control chip U2, controlled by the control unit 1, controls the on / off states of MOSFETs Q1 and Q2, chopping the DC 36V DC power supply on the primary side of transformer T3 and inverting it into a DC pulse voltage with continuously changing polarity. This voltage is then boosted from DC 36V to DC 1.8kV via transformer T3. A second boost is achieved through a 4x voltage multiplier shaping circuit composed of capacitors C3, C4, C5, C6, diodes D4, D5, D6, and D7, multiplying the DC 1.8kV to DC 7.2kV, which is then output. A resistor divider sampling circuit composed of resistors R12, R13, R9, and R10 converts the high-voltage DC 7.2kV into a low-voltage DC 7.2V signal, which is fed back to the control unit 1 to achieve real-time monitoring of the charging status.

[0035] The DC-DC boost unit 2 achieves a primary voltage boost through transformer T3 and a secondary voltage boost through a secondary boost module. While meeting the output voltage requirements, it reduces the number of transformers and the size of capacitors, thus satisfying the requirements for miniaturization and weight reduction. The overall volume of the DC-DC boost unit 2 can be as low as 0.0012m³. 3 Weighing as little as 1kg, its volume is 1 / 1250th that of a traditional DC-DC boost unit, and its weight is 1 / 100th that of a traditional DC-DC boost unit.

[0036] In an optional embodiment, the communication unit 4 may be a communication module, used to realize communication between the control unit 1 and the remote human-machine interaction unit 5, and to realize real-time interaction of input and output commands between the control unit 1 and the remote human-machine interaction unit 5.

[0037] In an optional embodiment, the remote human-machine interface unit 5 can be an industrial tablet PC, which is connected to the communication unit 4 via optical fiber. The remote human-machine interface unit 5 can be a box-type LCD touchscreen industrial tablet PC, enabling remote control of the impulse current generator via optical fiber communication, thus ensuring the safety of the operator. The operator can control the test parameters and test progress on the remote human-machine interface unit 5, and the test status can be displayed in real time on the display of the remote human-machine interface unit 5.

[0038] In an optional embodiment, the inrush current generating device further includes an LCD touch screen 6, a button 7, and an indicator light 8. The LCD touch screen 6, the button 7, and the indicator light 8 are electrically connected to the control unit 1, and the LCD touch screen 6, the button 7, and the indicator light 8 can be installed on the cabinet of the inrush current generating device.

[0039] Among them, button 7 and LCD touch screen 6 are used for command input, and indicator light 8 is used to display the working status of the impulse current generator.

[0040] The LCD touchscreen 6 can be a 5.7-inch thin-film transistor color touchscreen to realize the input of control commands and the display of test status. The LCD touchscreen 6 can transmit data with the control unit 1 through the RS232 serial communication interface.

[0041] The impulse current generating unit 3 can generate an impulse current waveform of 6.4 / 69μs, that is, an impulse current waveform with an actual wavefront time of 6.4μs and a half-value time of 69μs.

[0042] The impulse current generator provided by this utility model can be used for military helicopter testing to simulate the effect of lightning strikes on aircraft during severe convective weather, generating transient induced voltages or currents in the circuits or cables of airborne equipment for indirect lightning testing. It can generate a 6.4 / 69μs impulse current waveform, suitable for helicopter indirect lightning testing, meeting military standard testing requirements such as SAEARP5412A, SAEARP5416A, and RTCA / DO-160G S22. It can achieve a maximum pulse current output of 8kA; it can calibrate waveform parameters under various load conditions; its maximum inductive load capacity is 20μH, and its maximum resistive load capacity is 5Ω. It communicates with a remote human-machine interface unit via a communication module, enabling remote operation of the testing process, providing excellent human-machine interaction capabilities, fully ensuring the personal safety of operators, and possessing good transfer testing capabilities.

[0043] The above description is only an optional embodiment of this utility model. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of this utility model, and these improvements and modifications should also be considered within the protection scope of this utility model.

Claims

1. A surge current generating device, characterized by, It includes a control unit (1), a DC boost unit (2), an inrush current generating unit (3), a communication unit (4), and an indicator light (8). The control unit (1) is electrically connected to the DC boost unit (2), and the control unit (1) can control the DC boost unit (2) to output DC voltage. The control unit (1) is electrically connected to the impulse current generating unit (3). The impulse current generating unit (3) includes a short-circuit calibration circuit, a first on-load calibration circuit, and a second on-load calibration circuit. The control unit (1) is capable of switching between the short-circuit calibration circuit, the first on-load calibration circuit, and the second on-load calibration circuit. The output terminal of the DC boost unit (2) is connected to the input terminal of the impulse current generating unit (3), the output terminal of the impulse current generating unit (3) is connected to the short-circuit test line or the load under test, and the control unit (1) is connected to the remote human-machine interaction unit (5) through the communication unit (4). The indicator light (8) is electrically connected to the control unit (1).

2. The surge current generating device according to claim 1, wherein The impact current generating unit (3) includes resistor R1, capacitor C1, capacitor C2, switch K1, ignition gap switch G, switch K2, resistor R2, inductor L1, switch K3, resistor R3, resistor R4, inductor L2 and switch K4. The positive terminal of the input of the impact current generating unit (3) is connected to one end of the ignition gap switch G through resistor R1. The end of the ignition gap switch G connected to R1 is connected to the negative terminal of the input of the impact current generating unit (3) through capacitors C1 and C2 connected in parallel. Switch K1 and capacitor C2 are connected in series. The other end of the ignition gap switch G is connected to the positive terminal of the output of the impact current generating unit (3) via a first branch and a second branch connected in parallel. The first branch includes a switch K2, a resistor R2 and an inductor L1 connected in series. The second branch includes a switch K3, a resistor R3, a resistor R4 and an inductor L2 connected in series. A switch K4 is connected in parallel across the two ends of the resistor R4. The negative terminal of the input end of the impact current generating unit (3) is connected to the negative terminal of the output end of the impact current generating unit (3).

3. The surge current generating device according to claim 2, wherein The short-circuit calibration circuit includes resistor R1, capacitor C1, capacitor C2, ignition gap switch G, switch K2, resistor R2, and inductor L1; The first on-load calibration circuit includes resistor R1, capacitor C1, ignition gap switch G, switch K3, resistor R3, resistor R4, and inductor L2; The second on-load calibration circuit includes resistor R1, capacitor C1, ignition gap switch G, switch K3, resistor R3, and inductor L2.

4. The surge current generating device according to claim 1, wherein The DC boost unit (2) includes a pulse width control circuit, a push-pull inverter circuit, a DC voltage multiplier circuit, and a resistor voltage divider sampling circuit. The input terminal of the pulse width control circuit is electrically connected to the control unit (1). The output terminal of the pulse width control circuit is connected to the input terminal of the push-pull inverter circuit. The output terminal of the push-pull inverter circuit is connected to the primary side of the transformer in the DC voltage multiplier circuit. The primary side of the transformer is connected to a DC voltage. The output terminal of the DC voltage multiplier circuit is connected to the input terminal of the impulse current generating unit (3) as the output terminal of the DC boost unit (2). The output terminal of the DC voltage multiplier circuit is connected to the input terminal of the resistor voltage divider sampling circuit. The output terminal of the resistor voltage divider sampling circuit is connected to the signal input terminal of the control unit (1).

5. The surge current generating device according to claim 4, wherein The pulse width control circuit includes a PWM control chip U2; The push-pull inverter circuit includes field-effect transistors Q1 and Q2. The output terminal of the PWM control chip U2 is connected to the gates of field-effect transistors Q1 and Q2 respectively. The PWM control chip U2 can control the conduction and cutoff of field-effect transistors Q1 and Q2. The DC voltage multiplier circuit includes transformer T3, with a DC voltage connected to the primary side. The PWM control chip U2 can control the conduction and cutoff of MOSFETs Q1 and Q2 to invert the DC voltage on the primary side of transformer T3 into a DC pulse voltage. Transformer T3 then boosts the DC pulse voltage. The DC voltage multiplier circuit also includes a secondary boost module, which includes several capacitors and several diodes disposed on the secondary side of transformer T3. The secondary boost module boosts the voltage on the secondary side of transformer T3 twice and outputs it as the output voltage of the DC boost unit (2) to the inrush current generating unit (3).

6. The surge current generating device according to claim 1, wherein The impulse current generating unit (3) can generate a 6.4 / 69μs impulse current waveform.

7. The surge current generating device according to claim 1, wherein The remote human-machine interaction unit (5) is an industrial tablet computer, and the remote human-machine interaction unit (5) is connected to the communication unit (4) via optical fiber.

8. The impulse current generating device according to claim 1, characterized in that, It also includes an LCD touch screen (6), which is electrically connected to the control unit (1).

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