Smart Sensor Technology-Radio Frequency Sensors

Introduction:
The RF Smart Monitor System, shown in figure, is designed to allow the user to remotely collect machine vibration and temperature data without the need for cabling. This system, which is designed to monitor a wide variety of machine components, consists of following things:

--Battery-powered RF Smart Sensors, which are placed on machine components and collect/process vibration and temperature data,
--One or more RF Transceivers, each of which is able to remotely communicate with up to 64 RF Smart Sensors via radio,
--RBMware 4.20 or later to create the database and analyze the Smart Sensor data and,
--A CSI Model 2120 or Handheld Personal Computer (HPC) to communicate with RBMware and the RF Transceiver.

This system is designed to smoothly integrate with RBMware 4.20 or later. Databases and routes are created in RBMware and downloaded to the 2120 or HPC. Four measurement points (vibration, PeakVue, temperature, and battery life) are generated with each RF Smart Sensor created in RBMware. Once a route has been created, the user downloads this information into a 2120 or HPC. The user then connects the 2120 or HPC to the RF Transceiver and requests data from the remotely located RF Smart Sensors specified in the route. The RF Transceiver then transmits a message to the selected RF Smart Sensors directing them to collect and process the data based on analysis parameters established in RBMware. When complete, each RF Smart Sensor remotely transmits vibration, PeakVue, temperature, and battery life data back to the 2120 or HPC via the RF Transceiver. The collected data is then downloaded to RBMware for trending and analysis.

The RF Smart Monitor System is its wireless remote access capability. This is accomplished via a robust form of radio communications known as spread spectrum. This digital modulation technique has been widely used due to its immunity to interference. Spread spectrum systems are also very unlikely to cause interference with other radio systems, even other spread spectrum devices. Interference issues are minimized with this technique because the signal of interest is encoded with a lengthy digital pattern that approximates white noise. Consequently, the resulting signal looks like low-energy, band-limited white noise that can only be interpreted by a receiver that uses the same digital pattern to decode the signal. While the signal is relatively low power, long range communication is attainable due to the frequency of operation (2.4 GHz). The typical range achievable between an RF Smart Sensor and an RF Transceiver is approximately 300 feet. In addition, this form of communication does not require line-of-sight between RF Smart Sensors and RF Transceivers. This allows the RF Smart Sensors to be placed at the most ideal locations on the machine to maximize sensitivity to vibration and temperature signals. Another advantage of this modulation scheme is that no site license is required.

During the beta test phase of this product, RF Smart Monitoring Systems were evaluated at several industrial facilities on a variety of machines. One prime application of this technology highlighted during the testing phase is the use of this technology on machines that are either hard or dangerous to access. Machines in elevated locations (i.e. cooling towers) where the analyst was required to climb a ladder to reach the site, or machines located in hazardous locations (i.e. Class I, Div. II areas) are examples of such a scenario. Another use of this technology is on machines that have a range of motion (i.e., robots, accumulators, machine tools, cranes, etc.), where gaining access is difficult and routing cables is nearly impossible. Machines that fall in this category often are not analyzed for extended periods of time since they must typically be taken out of service prior to being surveyed. As this technology becomes widely used, other unique applications will undoubtedly be uncovered. In fact, the beta program highlighted new concepts that are now under consideration.

Capabilities of the RF Smart Sensors:
The RF Smart Sensor, whose construction is shown in figure consists of:

-- A high quality 10 mV/g accelerometer and temperature sensor
-- Analog circuitry to condition the vibration signal as well as generate a PeakVue Signal
-- Digital circuitry to process the vibration and temperature signals
-- An energy and power dense lithium C-cell battery for long life
-- A 2.4 GHz spread spectrum radio transmitter/receiver with antenna.

RF Smart Sensor battery life under normal conditions is expected to be one year or greater even with a full set of data being collected once per day. In addition, this device is mechanically designed to withstand the harsh conditions encountered in typical plant environments. Even with all the functionality built into the RF Smart Sensor, it is only approx. 4" tall and 2.5" in diameter.
In terms of measurement point setup, the RF Smart Sensor is capable of the following:

-- Vibration data displayed in acceleration, velocity, or displacement,
-- Pre-set sensor power on/off, measurement point sensitivity, and auto-ranging,
-- Single analog integration and double digital integration, and
-- Pre-set analog overall mode override.

All other measurement point setup options in RBMware are supported in the usual manner. In terms of analysis parameter setup, the RF Smart Sensor has the following capabilities:

--A series of pre-set Fmax values ranging from approx. 39 Hz to 9375 Hz (RBMware and the 2120 plotting functions will select the nearest Fmax which exceeds that of the RF Smart Sensor).
--Up to 1600 lines of resolution, ten averages, and twelve analysis parameters (Hz INT, Order INT, HFD, Hz vHFD, MP Wave, P-P Wave, and Crest), and
--Analog preprocessing with a fixed high-pass filter setting of 2.5 KHz.

Note that the RF Smart Sensor Fmax values in Hz are: 39.06, 58.59, 78.13, 117.19, 195.31, 191.97, 390.63, 585.94, 781.25, 1171.9, 1562.5, 2343.8, 4687.5, 6250.0, and 9375.0. Also note that spectral weighting, 1/3 octave analysis, SST, special time waveform collection, and demodulation in the envelope demodulator are not supported. All other analysis parameter options in RBMware are supported in the usual manner.

Finally, supported alarm limit set unit codes are VELOC, DISPL, ACCEL, HFD, TEMP (overall only), W-ACC, and W-VEL. Additionally, only the four absolute alarms are supported for the alarm type. All other alarm limit setup options are also supported. In this way this article described RF Smart sensors system, specifications, advantages of the modulation technique called spread spectrum.