Technical parameters and design of TIE47-3A dummy load

Dummy load It is a component, part or device that can replace the terminal to receive electrical power in a circuit (such as an amplifier) ​​or an electrical appliance output port. Dummy loads are usually used to test the power of long-wave, medium-wave and short-wave broadcast transmitters. The maximum power dissipation of the TIE47-3A (AK57 SLB) dummy load is 750 kW, which can be used for power testing of transmitters with a carrier power of 500 kW; the auxiliary equipment of the TIE-47-3A dummy load includes a wind-water heat exchanger and a three-way valve with electronic temperature control.

The power consumed by the dummy load of TIE47-3A usually depends on the temperature and flow rate of the soda water in the soda water loop. In this closed soda water loop, the most important part is the soda water resistance, and it is required to have a relatively constant impedance in the wide frequency range of 30 Hz to 30 MHz.

The soda water circuit of TIE47-3A is connected to the wind-water heat exchanger through a three-way valve driven by a motor. The three-way valve can then be adjusted manually or automatically through the control button on the panel to control the flow of soda water entering the heat exchanger, so that the average temperature of the soda water remains basically constant. The flow monitor and temperature protection switch installed in the soda water circuit can be connected to the interlocking circuit of the transmitter control system as a safety protection device. The threshold value of the temperature protection switch is 85°C. When the soda water temperature exceeds 85°C, the temperature protection switch will be disconnected, causing the transmitter control system to be interlocked and eventually shut down the transmitter power system.

1 Technical parameters and design operation methods of dummy load

1.1 Technical parameters

The main technical parameters of TIE47-3A are as follows:

◇Power: 750kW;

◇Frequency range: 30Hz～30MHz:

◇Resistance: 300 ohms balanced;

◇Maximum VSWR: less than 1.2 at 26MHz; less than <1.83 at 100MHz:

◇RF power measurement is carried out using a calorimeter.

In addition, the main technical parameters of its soda water circuit are:

◇Flow meter flow range: 2500～25000l/h;

◇When the normal temperature is about 26℃, the flow rate set for 750kW is 25000l/h;

◇The average temperature of inlet and outlet water is about 70℃;

◇Water pump motor voltage: 3∮ 380V/50Hz;

◇The water pump motor power consumption is about 5.1 kW;

◇The total amount of soda water is about 250 L.

1.2 Design and operation

The principle of the soda water circuit of TIE47-3A is shown in Figure 1. In the figure, the soda water flows out from the water tank A21 (3/4 full), then passes through the water pump A24 and the heat exchanger A122 to the resistor R10, and then passes through the

Flow monitor A26, flow meter A12, temperature control protection switch A7, and then return to the water tank A21. Figure 2 shows the dummy load interlock line of TIE47-3A. Among them, R10 is a virtual resistor, which is used in Figure 2 to represent the equivalent water resistance of soda water.

The flow rate of soda water is controlled by valve A15. Flow meter A12 works according to the principle of magnetic induction. The measurement tolerance of the full scale value is 1.2%. The set flow value can be checked at any time during operation and should be corrected when necessary.

The temperature control protection switch A7 and flow monitoring switch A26 in the circuit of Figure 1 are used to protect the soda water resistor R10. They must be connected to the interlock circuit of the transmitter control system. When the soda water stops circulating or the soda water temperature is too high, A26 should be able to shut down immediately.

The temperature controller and the operating switch S60 are installed in the control box as shown in FIG3 . The switch S60 has four selection positions, which can control the three-way valve A5 to be OFF (0), Auto (automatic), Open (↑), and Closed (↓). If the operation mode is in the "Auto" position, the temperature controller will automatically control the three-way valve A5 to adjust the flow of soda water entering the heat exchanger for cooling, thereby adjusting the temperature of the soda water so that the average temperature of the soda water remains basically constant. The "Open" and "Closed" positions are used to manually adjust the three-way valve. When Open (↑) is selected, the three-way valve is opened, and the soda water is bypassed without passing through the heat exchanger; when Closed (↓) is selected, the three-way valve is closed, and the soda water flows through the heat exchanger for cooling. The OFF (0) position will close the three-way valve control circuit.

The three-way valve A5 is used to adjust the ratio of the soda water flow rate in the heat exchanger to the soda water flow rate in the bypass, so as to adjust the average temperature of the soda water to about 70°C. For example, when adjusting the machine, the transmitter power is added to the dummy load. In order to match the dummy load impedance with the transmitter output impedance (300Ω after the variable resistance line), the soda water temperature of the dummy load must be controlled at about 70°C (at 70°C, the soda water resistance is 300Ω). In fact, by changing the soda water flow rate flowing through the heat exchanger for cooling through the three-way valve A5, the temperature of the soda water can be adjusted to an appropriate temperature.

When operating, please pay attention to the maximum allowable power that the dummy load can convert. In addition, the dummy load can be changed to other resistance values ​​(such as 50 ohms, unbalanced dummy load) according to needs, or the standing wave ratio can be changed to: 30MHz<1.1, 250 MHz<1.5 (50 ohms, unbalanced dummy load). At the same time, the amount of soda water required depends on the installation size. The amount of water in TIE47-3A is about 3Kg of anhydrous soda (Na2CO3).

2. Installation of dummy load

A tap and drain should be reserved near the installation point of the dummy load. If the dummy load is overhauled, the soda water must be drained and the entire pipe system (including the soda water tank A21) must be rinsed with tap water. At the same time, acid must be used to neutralize the soda water (for corrosion prevention).

During installation, the dummy load can be fixed on the ground; then install the electric control box A100, connect the power supply and feeder, and connect the cooling water source and the exhaust hole of the cooling water circuit (the exhaust hole screw is installed on the top of the soda water heat exchanger A122); in addition, it should be noted that the ground wire of the dummy load should be connected to the RF ground grid.

3 Debugging of dummy load

The soda water resistor R10 can only be connected to AC voltage. If it is connected to DC voltage, explosive gas will be generated!

When debugging TIE47-3A, you can first add water to the water tank of the dummy load. The water should be added to 3/4 of the water tank, so that space can be reserved for the soda water returned from the heat exchanger. Then disconnect the soda water resistor R10 from the feed core, and then use S10/S20 to turn on the test load. When testing, set the mode selection switch S10 to the "LOCAL" position, set the water pump switch S20 to "ON", then start the soda water circulation pump, and open the A15 valve.

After that, set the temperature control switch S60 to the "Open" position, let the three-way valve run in the middle position, and then set the S60 switch to the "OFF" position. Then adjust the valve A15 to adjust the flow rate of the flowmeter A12 to 27 m3/h. Then add soda and set the soda water resistance value according to the soda water resistance curve shown in Figure 4. Then use the volt-ampere method to measure the soda water resistance value. During the test, the 220 V AC phase line can be connected to one electrode of the dummy load through an ammeter (the multimeter is set to the AC current range), the neutral line is connected to the shell of the dummy load, and the power ground line is also connected to the shell of the dummy load. Then a voltmeter (the multimeter is set to the AC voltage range) is connected to the output end of the ammeter. Finally, the resistance value of the soda water is calculated using Ohm's law (R=U/I).

The interlock line of the dummy load must be connected to the transmitter's locking system. The functions of all devices in the interlock loop should be tested and then the correct threshold or shutdown point should be set.

After that, remove the voltammetry measurement wire, restore the connection between resistor R10 and the feed core, and use the transmitter power for heating (if a heating resistor is installed in the soda water tank, the heating resistor can also be used for heating) to set the center temperature of the temperature controller A3 to 70°C so that the soda water reaches an average temperature of 70°C.

Next, turn off the transmitter and disconnect the dummy load from the feed core, and test the resistance value of R10 after heating again. When the soda water reaches an average temperature of 70°C, the resistance value of R10 measured according to the wiring method shown in Figure 5 should be about 150Ω.

Finally, turn off the transmitter and set the mode selection switch S10 to the "OFF" position to turn off the dummy load.

When maintaining the dummy load, it is recommended to run the dummy load at no load (without transmitter power) for about 1 hour every week to allow the crystallized soda to mix and dissolve with water again.

The other components of TIE47-3A generally do not require special maintenance, but the heat exchanger should be cleaned and inspected regularly, especially the condenser fins should not be blocked by dirt, and can be cleaned with a high-pressure water gun.

4 Conclusion

The transmitter output power is added to the soda water resistor of the dummy load, and then the power is measured and calculated by the calorimetric power measurement unit. The measured soda water flow rate and the temperature of the water inlet and outlet of the soda water resistor are sent to the power meter, and the dummy load can be functionally equivalent to the load. However, this is not actually composed of a real load, but a resistor acting as a certain load. This method is more commonly used in microwave radio frequency, and a dummy load is usually loaded for simulation during the debugging stage.