Fluke 125 Portable Oscilloscope Scopemeter

Industrial manufacturing processes and plant control are connected through a digital network. Industrial digital networks function in very harsh environments which are constantly exposed to high humidity, a variety of chemicals, and abrupt temperature changes. Determining if a network problem is with electrical signaling, the digital protocol, or the cabling can be extremely frustrating without the right measurements and tools. Maintaining these industrial networks requires accurate measurements and reliable troubleshooting methods.  

Capacitance and Resistance measurements.

Troubleshooting a network segment begins with checking connectivity, then measuring the cable impedance to make sure it is not shorted or open. Cable impedance is dependant on the network type, for example, Foundation Fieldbus uses a 120 Ohm cable terminated at either end of the segment with 120 Ohms. Also, check capacitance, making sure it is within specification. A good cable is essential for proper electrical signal performance.

Network signal electrical performance.

Checking electrical signal performance requires measuring key parameters of the network signal. The 125 includes a Bus Health test mode that is designed to capture and trigger on network signal waveforms. Select a bus type, the ScopeMeter Bus Health mode then runs algorithms to measure key signal parameters like signal low bias voltages, bias voltages, high and peak to peak levels. The bus health mode also measures signal jitter or distortion to determine overall signal quality.

Verify signaling meets specification.

The signal parameter measurements are compared to industry specifications, a high and low limit defined by the standard is used to evaluate if these key parameters are within specification. Display icons are used to indicate which parameters are outside of the industry specification.

Incorrect or Fluctuating bias voltages is characteristic of termination or grounding issues, while low signal level measurements could mean there is excessive attenuation caused by too many devices on one segment, an incorrect network termination, or too long cable runs. Signal distortion like overshoot is a sign of reflections usually caused by failing connectors or cable imperfections.

Inspecting the signaling for disturbances is simplified with the eye pattern display mode. The clearer the center eye of the signal display the less disturbances and distortion on the signal. Jitter and Phase noise are typical digital signal distortion caused by device receiver transmitter circuits. External electrical interference from high energy sources such as heavy duty machinery and lighting systems can be detected by inspecting the eye pattern.

Electrical interference such as transients, static discharge, and noise may cause network devices to reset, so monitoring a segment can capture these events thereby helping to isolate their source.

Once the signaling parameters and cabling are eliminated, network protocol diagnostic tools are used to verify digital protocol performance. Go to www.flukenetworks.com to learn more about network diagnostic solutions.

Eliminating signal quality issues and cabling are 2 critical steps to isolating performance and network issues. The Fluke 125 ScopeMeter includes algorithms and measurement functions to verify the integrity of network digital signaling.