Practical Industrial Data Networks:Design, Installation and ...

MultimeterDeviceNet overview 175A multimeter capable of measuring DC volts, resistance, and current is an indispensabletroubleshooting tool. On the current scale, it should be capable of measuring severalamperes.OscilloscopeAn inexpensive 20 MHz dual-trace oscilloscope comes in quite handy. It can be used forall the voltage tests as well as observing noise on the lines, but caution should beexercised when interpreting traces.Firstly, signal lines must be observed in differential mode (with probes connected toCAN_H and CAN_L. If they are observed one at a time with reference to ground, theymay seem unacceptable due to the common mode noise (which is not a problem since it isrejected by the differential mode receivers on the nodes).Handheld analyzersHandheld DeviceNet analyzers such as the NetAlert NetMeter or DeviceNet Detectivecan be used for several purposes. Depending on the capabilities of the specific device,they can configure node addresses and baud rates, monitor power and signal levels, logerrors and network events of periods ranging from a few minutes to several days, indicateshort circuits and poorly wired connections, and obtain configuration states as well asfirmware versions and serial numbers from devices.Figure 12.23NetAlert NetMeterIntelligent wiring componentsExamples of these are the NetAlert traffic monitor and NetAlert power monitor. Theseare ‘intelligent’ tee-pieces that are wired into the system. The first device monitors anddisplays network traffic by means of LEDs and gives a visual warning if traffic levelsexceed 90%. The second device monitors voltages and visually indicates whether they areOK, too high, too low, or totally out of range.