Principle and parameters of vacuum degree tester

Test principle

Open the two contacts of the arc extinguishing chamber to a certain distance, apply pulse high voltage, surround the electromagnetic coil outside the arc extinguishing chamber, and pass a large current to the coil, thereby generating a pulse magnetic field in the arc extinguishing chamber that is synchronized with the high voltage. In this way, under the action of the pulse magnetic field, the electrons in the arc extinguishing chamber make spiral motions and collide with the residual gas molecules for ionization. The resulting ion current is approximately proportional to the density of the residual gas, that is, the degree of vacuum. For different vacuum tubes, under the same vacuum degree conditions, the magnitude of the ion current is also different. After the ion current is measured, the computer automatically calculates the vacuum degree through the ion current-vacuum degree curve and displays the vacuum degree value.

◆Treatment of leakage current

When high voltage is applied to both ends of the vacuum interrupter in the disconnected state, there will be a leakage current of several microamps with varying values. This leakage current has large individual differences even among vacuum interrupters of the same model. Especially for the vacuum arc extinguishing chamber installed on the whole machine, since the insulating supports around it also have leakage, the sum of these leakages is more unstable and unpredictable, and is numerically on the order of 10-4Pa. The ionization current of a vacuum interrupter is comparable. We use the method of starting the high voltage twice to deduct the leakage current and ensure the accuracy of vacuum measurement whether it is installed on the whole machine or the vacuum interrupter to be installed.

◆Built-in multiple measurement curves for vacuum interrupters

Due to the different geometric dimensions and materials of the vacuum interrupter, when the internal vacuum degree and external excitation power supply are constant, the amount of discharge charge is different, and there is a considerable difference. For accurate measurement, each type of vacuum interrupter must have a corresponding projection curve from the amount of ionization charge to the degree of vacuum. Through close cooperation with major domestic vacuum interrupter manufacturers, our factory's experts have obtained a lot of data on the relationship between the ionization charge and vacuum degree of vacuum interrupters, and through mathematical processing, their characteristic parameters are fed into the product. Therefore, many measurement curves of vacuum interrupters are built into the product.

◆Perfect input protection circuit

When the vacuum degree of the vacuum interrupter is very low, the vacuum interrupter will be broken down by high voltage during measurement, and the instantaneous high voltage is directly added to the sampling circuit at the signal input end, causing it to withstand a very strong electrical impact. The sampling circuit at the signal input end has a complete protection circuit added. Even if the instrument temporarily fails to work properly due to a high-voltage impact at the input end (just restart it), the circuit will not be damaged.

Technical Parameters:

1. Vacuum measurement range: 1×10-1～1×10-5

2. Measurement error: <10%

3. Measurement resolution: 10-5pa

4. Allowable ambient temperature: -20℃～50℃

5. Air humidity: ≤80%RH

6. Power supply: AC, 220V, 50Hz±10%

7. Overall dimensions: 420×290×210 (mm)

8. Weight: 8kg