A Monitoring System for Condition-based Maintenance without Laying New Communication Cables

By applying condition-based maintenance (CBM), monitoring points are expected to be increased. Toshiba developed a new monitoring system used for condition-based maintenance (CBM) with minimal cost. This system allows plant personnel in the control room or plant office to monitor plant equipment by video images and real-time sensing data, such as vibration, without laying new communication cables. Figure 1 shows the system configuration. The system uses existing device control cables for data transmission. The transmitter modulates the video or sensing signals, and superimposes the modulated signals on the device control signals over the existing cables; the receiver separates the modulated signals from the control signals, and demodulates the signals. The system analyses the video images and sensing data, such as vibration, and detects abnormalities of rotating machines, valves, or piping. This system supports plant equipment integrity by early detection of abnormality, and eventually contributes to maintenance cost reduction.

 

 

 

 

 

(1) Components
Plant equipment (Rotating machines, valves and piping, etc)

(2) Condition
Existing cables such as the control cables and the switching cables can be used for transmission of monitoring data.

 

(1) Existing cables are used for transmission of monitoring data.
The monitoring data is transmitted to the office or control room, by just connecting the transmitter and receiver with existing cables.

(2) Various monitoring devices can be connected to the system, for examples;
・Video Camera (with direction control)
・Vibration transducer (accelerometer, proximity probe, etc)
・Process sensors (pressure gage, flow meter, etc)
・Any sensors that provide voltage outputs

(3) The transmitter and receiver are designed not to influence the control signal or switching signal. The level of modulated signals is sufficiently low compared with the control signal as shown in Figure 4.

(4) The signal transmission doesn't influence instrumentations because electric field strength caused by monitoring signal transmission is below a regulated value, VCCI-class A.
      VCCI: Voluntary Control Council for Information Technology Equipment

Figure 1 shows the transmitter, network camera, and wireless accelerometers. Specification of each device is shown in Table 1.

 

 

 

 

Transmitter and receiver
Transmission distance	Max. 900m
Transmission speed	Max. 30Mbps
Moderation	DMT(Discrete Multi Tone)
Carrier frequency	30kHz~1.1MHz
Size	225*165*40mm Transmitter
	260*190*84mm Receiver
Camera
Type	Network camera (built-in web server)
Image compression	JPEG (Motion JPEG)
Zoom	21×(Optical) , 2×(Digital)
Pan	±175 deg
Tilt	＋90 deg～－120deg
Wireless accelerometer
Radio frequency	303MHz
Transmission distance	Max. ～15m
Number of sensors	Max. 250
Sensor	Piezoelectric accelerometer with internal electronics    Frequency：～14kHz、Range：±10G
Signal processing	A/D 10bit    Sampling frequency：256/1.28k/2.56kHz    Sampling data：512/1024 points

 

 

 

Examples of application are shown below.

(1) Figure 5 shows an example, where signals are transmitted over a limit switch cable of a motor operated valve (MOV) installed in a plant test loop. Video image and vibration data are transmitted with satisfactory quality and response time. Figure 6 shows sample video image. In the actual system, an operator can control camera angle and zooming, to confirm the meters and leaking point. The applicability evaluation to the actual plant is planned in the near future.

 

 

 

 

 

(2) Condition monitoring equipments in Pressure Containment Vessel (PCV) of nuclear plants (Figure 7) The monitoring signals can be transmitted without using additional electrical penetration assembly.