Commissioning – Tips & Tricks
It is much easier to break commissioning into parts.
Radio test
Use portable units to test the radio path. Usually this consists of using the same wireless units powered by a couple of batteries and temporarily installed antennas. Testing the radio path prior to installation minimizes the risk of having to change the antenna installation on commissioning.
Most modern wireless devices provide a readout of both received signal strength (normally referred to as “RSSI”) and background noise level. Record these measurements to assist with future troubleshooting. If the wireless link commissions well but fails later, comparing the RSSI and noise figures with the “as-commissioned” figures gives a good indication of the problem.
A significant drop in signal level indicates that less RF power is being radiated at the transmitter (moisture in the cable or antenna, low voltage at the transmitter or transmitter fault), or the radio path has changed (trees now have leaves, another obstacle in the radio path, antennas have moved).
A significant increase in noise level indicates that other RF transmitter are active close by.
Bench test
Test the configuration of the system on the bench before installing the equipment. If the system works well on the bench, but not after installation, then the difference is the radio side of the system. Make sure that you bench test without antennas; connecting antennas will cause the receivers to saturate.
How to improve radio performance? Here are some tips:
- If background noise level is high, try to locate the cause of the interference. Is there a nearby antenna causing interference? Is the antenna installed close to noisy equipment such as variable frequency motor drive?
- Increase the RF signal level as much as possible.
- Try moving the antenna. If there is multi-path fading in an industrial plant or factory, then the antenna may only need to be moved a short distance to one side. In longer distance application, increase the height of the antenna to clear obstacles.
- Increase transmitter power if this is possible (but do not exceed regulation). Increase antenna gain or decrease cable loss, but again, do not exceed ERP regulations. If the wireless system is a one-way link (transmitter to receiver), you can increase the antenna gain at the receiver without worrying about ERP limits at the transmitter.
- If it is not possible to establish a reliable radio path, can you use an intermediate repeater? Most industrial wireless products have a “store&forward” repeater function where wireless messages can be received and re-transmitted on to other units in the network.