**4. Application of the AE technique to klystron tubes**

The results presented in this section were obtained at the Naval Surface Warfare Center, Port Hueneme Division, Dam Neck Detachment (NSWC PHD DN), and the Fleet Training Center (FLETRACEN) San Diego [6]. A simplified description of the field test unit utilized in these experiments is shown in **Figure 1**.

The radar system utilized during this test was the AN/SPS49 (V)5 radar with a 5-cavity klystron amplifier. The pulse repetition frequency (PRF) was set at 213 pps. This unit typically generates two pulses with durations of 2 and 125 μs, respectively. This klystron unit had 48 channels between 851 and 942 MHz. Channels 1–16 cover the low band; channels 17–32 cover the middle band; and channels 33–48 cover the high band. Channel 8, with a center frequency of 894.33 MHz, was frequently utilized

**Figure 1.** *Simplified field test unit.*

**47**

**Figure 4.**

**Figure 3.**

*Automated Classification of Microwave Transmitter Failures Using Virtual Sensors*

*Signature signals from acoustic and cathode current sensors at 45° waveguide bend, location 6.*

*Signature signals from acoustic and cathode current sensors at RF isolator, location 8.*

in this experiment. The klystron unit was connected to a dummy load at the end of the waveguide. The dummy load was cooled by circulating water. During normal operation, the cathode was held at −42 kV with respect to the grounded collector.

The cathode current sensor was connected directly to the control panel of the radar transmitter. The acoustic emission system included a general-purpose R50 transducer, a preamplifier, and a post amplifier, all supplied by Physical Acoustics Corporation. **Figure 2** shows the different locations on the radar, denoted by black squares, where the AE transducer was attached in order to collect the acoustic emissions generated during normal and abnormal stressed operation. Locations include the coax, low pass filter, RF isolator, and several portions of the waveguide. A LeCroy 9354AM 500 MHz digital oscilloscope was used to detect and store signals from the generated acoustic emission, the input (RF drive) of the klystron amplifier, and the beam current sensor. **Figures 3** and **4** show typical signature signals from the sensors for the AE detection of the RF pulse and the cathode current (CC) for different locations on the klystron system under normal operation. These plots show the strong correla-

*DOI: http://dx.doi.org/10.5772/intechopen.81652*

tion between acoustic emission and RF emission.

**Figure 2.** *Sensor location on klystron system.*

#### *Automated Classification of Microwave Transmitter Failures Using Virtual Sensors DOI: http://dx.doi.org/10.5772/intechopen.81652*

in this experiment. The klystron unit was connected to a dummy load at the end of the waveguide. The dummy load was cooled by circulating water. During normal operation, the cathode was held at −42 kV with respect to the grounded collector.

The cathode current sensor was connected directly to the control panel of the radar transmitter. The acoustic emission system included a general-purpose R50 transducer, a preamplifier, and a post amplifier, all supplied by Physical Acoustics Corporation. **Figure 2** shows the different locations on the radar, denoted by black squares, where the AE transducer was attached in order to collect the acoustic emissions generated during normal and abnormal stressed operation. Locations include the coax, low pass filter, RF isolator, and several portions of the waveguide. A LeCroy 9354AM 500 MHz digital oscilloscope was used to detect and store signals from the generated acoustic emission, the input (RF drive) of the klystron amplifier, and the beam current sensor.

**Figures 3** and **4** show typical signature signals from the sensors for the AE detection of the RF pulse and the cathode current (CC) for different locations on the klystron system under normal operation. These plots show the strong correlation between acoustic emission and RF emission.

**Figure 3.**

*Acoustics of Materials*

Seal failures and inverse pulses are termed as transient events causing tube

The results presented in this section were obtained at the Naval Surface Warfare Center, Port Hueneme Division, Dam Neck Detachment (NSWC PHD DN), and the Fleet Training Center (FLETRACEN) San Diego [6]. A simplified description of the

The radar system utilized during this test was the AN/SPS49 (V)5 radar with a 5-cavity klystron amplifier. The pulse repetition frequency (PRF) was set at 213 pps. This unit typically generates two pulses with durations of 2 and 125 μs, respectively. This klystron unit had 48 channels between 851 and 942 MHz. Channels 1–16 cover the low band; channels 17–32 cover the middle band; and channels 33–48 cover the high band. Channel 8, with a center frequency of 894.33 MHz, was frequently utilized

**4. Application of the AE technique to klystron tubes**

field test unit utilized in these experiments is shown in **Figure 1**.

**3.4 Other**

failures.

**46**

**Figure 2.**

**Figure 1.**

*Simplified field test unit.*

*Sensor location on klystron system.*

*Signature signals from acoustic and cathode current sensors at 45° waveguide bend, location 6.*

**Figure 4.** *Signature signals from acoustic and cathode current sensors at RF isolator, location 8.*

#### *Acoustics of Materials*

A threshold amplifier was used to discriminate between normal and anomalous current pulses. Further details of the experiments can be found in Ref. [6].

Anomalous pulses were generated by several methods, including increasing the klystron voltages above normal operating specifications, up to 45 kV. This increase in voltage generated anomalous cathode current and acoustic pulses. **Figure 5** shows a typical anomalous current pulse under stress conditions.

**Figure 6** shows a detection of a fault in the system induced by stress conditions. An anomalous cathode current pulse was detected. The corresponding acoustic emission pulse shows a slight increase in the detected acoustic signal. **Figure 7** shows the detection of a very different type of fault. In this case, an anomalous cathode current pulse was detected during a crowbar fault but no acoustic emission was detected. In this case, a catastrophic failure of a modulator tube was responsible for the fault. The absence of acoustic energy along with the detection of an

**Figure 5.** *Anomalous current pulse under stress conditions.*

**49**

*Automated Classification of Microwave Transmitter Failures Using Virtual Sensors*

anomalous cathode current pulse provides a possible signature for modulator tube failure. The system demonstrated the ability to discriminate between normal and anomalous pulses in klystron devices using current and acoustic sensors, and it showed a correlation between the two types of detection. The system also demon-

This section presents the effects on AE during normal and abnormal functioning of a magnetron. The experiment was conducted at the SPAWAR Systems Center, San Diego microwave radar tube laboratory [7]. The proper operation of a magnetron device depends upon the amplitude of the pulsed voltage applied, the temperature, the filament voltage, and the proper loading of the magnetron by the RF system. The normal operating parameters of the magnetron tube (2J55) utilized for this experiment were intentionally changed in order to stress the magnetron tube and induce abnormal functioning. **Table 1** shows the magnetron parameters

It was observed that when the tube was stressed, it typically produced an anomalous current pulse with a resulting anomalous RF pulse. The pulses were captured utilizing the masking feature of a 500-MHz digital LeCroy 9354AM oscilloscope, where a mask is defined based on a normal pulse shape, and pulses which lie outside the mask are captured. A fast Fourier transform was performed on the

**Figures 8** and **9** were obtained by using a type S9208 AE transducer, and they show the normal and abnormal pulses, respectively. In both cases, the pulse rate was adjusted to 100 pps, and the oscillator filament primary voltage was set at the normal value of 115 V. Channel 3 on the oscilloscope was connected to the output of the acoustic emission post amplifier and is shown in the upper trace. Channel B was connected to the current sensor of the magnetron, and it shows a zoom trace of the current pulse (see lower curve in figures). The mask was set on channel D

strated the ability to characterize different types of failures.

**5. Application of the AE technique to magnetron tubes**

for the experiments described below.

*Fault detection: anomalous current pulse with no AE.*

captured AE signal.

**Figure 7.**

*DOI: http://dx.doi.org/10.5772/intechopen.81652*

**Figure 6.** *Fault detection: anomalous current pulse with corresponding change in AE.*

*Automated Classification of Microwave Transmitter Failures Using Virtual Sensors DOI: http://dx.doi.org/10.5772/intechopen.81652*

**Figure 7.** *Fault detection: anomalous current pulse with no AE.*

*Acoustics of Materials*

A threshold amplifier was used to discriminate between normal and anomalous

Anomalous pulses were generated by several methods, including increasing the klystron voltages above normal operating specifications, up to 45 kV. This increase in voltage generated anomalous cathode current and acoustic pulses. **Figure 5** shows

**Figure 6** shows a detection of a fault in the system induced by stress conditions. An anomalous cathode current pulse was detected. The corresponding acoustic emission pulse shows a slight increase in the detected acoustic signal. **Figure 7** shows the detection of a very different type of fault. In this case, an anomalous cathode current pulse was detected during a crowbar fault but no acoustic emission was detected. In this case, a catastrophic failure of a modulator tube was responsible for the fault. The absence of acoustic energy along with the detection of an

current pulses. Further details of the experiments can be found in Ref. [6].

a typical anomalous current pulse under stress conditions.

**48**

**Figure 6.**

**Figure 5.**

*Anomalous current pulse under stress conditions.*

*Fault detection: anomalous current pulse with corresponding change in AE.*

anomalous cathode current pulse provides a possible signature for modulator tube failure. The system demonstrated the ability to discriminate between normal and anomalous pulses in klystron devices using current and acoustic sensors, and it showed a correlation between the two types of detection. The system also demonstrated the ability to characterize different types of failures.
