Wireless Data Collection Technology Explained
August 27, 2007
Quality control professionals, inspectors and machinists have a new cost-effective, reliable option for maintaining wireless data integrity. A complete, robust wireless data collection system that uses a wireless mesh network offers many advantages over conventional data collection.
Wireless systems deliver their quality or production data to critical operations downstream and are crucial components of the modern production reality. The advantages of a wireless data collection system include the ability to significantly reduce human error in data recording. It also removes wiring-related placement, installation, safety and cost issues. And, it makes it easier to bring a precision measuring tool to the work, rather than bringing work to the measuring tool.
Wireless data transmission is critical for improving quality on the shop floor, but some wireless systems are vulnerable to shop-induced interference. Radio frequency (RF) waves are the carrier for data in a mesh network wireless data acquisition system. These waves are simply energy propagated through free space. When free space is cluttered with other energy forms, intentional radio waves are compromised.
RF is highly susceptible to corruption and alteration via a variety of electromagnetic interference (EMI). EMI has been defined as the “degradation of the performance of a piece of equipment, transmission channel, or system caused by an electromagnetic disturbance” according to ANSI C63.14. EMI can occur throughout the EM spectrum from 0 Hz to 20 GHz or higher frequencies.
However, EMI problems are most prevalent in the RF spectrum. EMI types typical of, but not limited to, production shop environments including DC fields-quasi-AC fields and magnetic, AC fields and, RF and transient electromagnetic fields. Regardless, good RF design practice must be built into a system to keep the data intact during wireless data transmission.
In the presence of these EMI components, RF-based systems must manage their performance relative to interference if they are to be useful. There is no such thing as a 100% noise immune radio system. So with that truth, systems designers must develop robust wireless data collection networks and sensors that are less susceptible to the presence of EMI.
Design a Better NetworkThere are many techniques that designers can use to offset the impact of noise in a wireless network. One such technique is to create a robust and reliable wireless network by setting up a mesh network.
A mesh network is a topology that has some distinctive features. First, it has a single and central gateway function where all systemwide commands and network management can occur. Data from the network also returns here. Secondly, the sensor/measurement endpoint radios can be active components of the network. Thirdly, numerous routers or repeaters are present and can be added to enable multiple paths for over the air (OTA) transmissions.
he mesh is inherently robust to interference by the very nature of the system configuration. An example of this can be explained by looking at what happens to the OTA flight of the RF. The endpoint radio acquires data from its measurement tool or sensor, and then transmits it to the gateway. A plume of EMI from an induction hardener cancels the RF in the immediate vicinity.
Adjacent to the first router, other routers also have received the data transmission. After the blocked router has found no data was received, it cannot pass along any data to the gateway. Simultaneously, the other routers have the good data and attempt to send that data to the gateway.
The data may make a series of router hops until it reaches the gateway. While this is happening, other copies of the data are en route to the gateway. When the gateway sees an exact copy of already received data, the gateway discards the additional copies. Endpoint radios on the network have a unique address that allows only the intended data to reach the gateway without duplication.
In addition, when EMI is not present and optimal operating conditions exist, the mesh network speeds OTA transmission by constructing a routing table in each network element. The router table creates a predetermined path for data that allows the other routers in the network to be either idle or available for other endpoints to communicate through them.
Multiple paths in a mesh network provide alternative paths for data, thus spatially and temporally avoiding corruption from EMI.
Unlike mesh networks, daisy chain or point-to-point networks suffer from single points of failure. If one link in the chain is corrupted via EMI, then OTA transmission will stop at that break in the chain.
If the wireless network is capable of supporting a mesh configuration, then simply adding routers to the system will make the system more robust.
Designing and implementing a wireless mesh network is one way to offset the impact of noise and to achieve reliable performance and data from a wireless data collection system. Operators in today’s hostile manufacturing environments can benefit from using this technology to ensure high data integrity. Q
Tech TipsA mesh network is a topology that has some distinctive features:
- It has a single and central gateway function where all systemwide commands and network management can occur. Data from the network also returns here.
- The sensor/measurement endpoint radios can be active components of the network.
- Numerous routers or repeaters are present and can be added to enable multiple paths for over the air transmissions.