Tag Archives: Analog Devices

MEMS Vibration Sensor

Analog Devices Inc. has unveiled their MEMS or Micro-Electro-Mechanical System-based accelerometer technology at the Sensors + Test Conference in Nuremberg, Germany. The MEMS vibration sensor can track vibrations at frequencies of 22 kHz. This is especially helpful for sensing high-frequency vibrations in industrial equipment.

The MEMS technology from Analog Devices is unique in the sense that it uses two MEMS mechanisms placed beside each other. The arrangement helps to cancel out common mode noise, favoring only the differential mode noise. Vibration and shock sensors from ADI are small format sensors that enable equipment designers to build vibration-detection chips within devices for industrial process-control, rather than as add-on modules.

Most vibration sensors today are piezo-electric-based modules. They have two disadvantages—it is not possible to mass-produce them, and their range is limited to 5-kHz frequencies. On the other hand, ADI makes their accelerometers in CMOS processing lines, and they can mass produce them easily. Additionally, ADI can undercut the prices of piezo-based vibration sensors by about 50 percent. For instance, the prices of ADI vibration sensors are around $35 as opposed to piezo-based sensors at $70.

With manufacturers looking for whatever they can get for improving the production and efficiency of their equipment, MEMS vibration sensors from ADI are the right products in the right place and at the right time. Although, when comparing unit shipments, the industrial market is small compared to the consumer electronics market, revenue-wise, the former is incredibly important and offers better margins. MEMS sensors address identified needs within the industrial market sector, and therefore, provide tangible value.

In the case of piezo-based vibration sensor modules, the standard practice is to bolt them onto the side of vibrating industrial equipment. However, using the chip-based accelerometer sensor from ADI is simpler, as it is possible to integrate it right within the circuit board of the device when assembling. ADI is of the opinion that some piezo-based vibration sensor manufacturers may retrofit MEMS chips into their bolt-on modules. However, ADI also expects OEMs of industrial equipment to stop using modules and rather start integrating ADI MEMS chips directly into their pumps, motors, gearboxes, and other pieces of industrial equipment.

Industrial equipment manufacturers are increasingly using vibration sensors as these can sense on-coming failure before it happens. For instance, a deteriorating bearing will vibrate at high frequencies before it fails. As it nears failure, its vibrating frequencies will drop until it finally disintegrates totally, possibly causing damage to the rotor. This is why predictive maintenance is increasingly becoming popular.

The present trend in the industry is to move towards predictive maintenance from preventive maintenance. Early detection through predictive maintenance can cut down repair costs by as much as 25 percent. Waiting to repair equipment until something fails can push up the maintenance costs more than ten times. Compared to other predictive maintenance techniques such as ultrasonic analysis or infrared thermography, vibration analysis offers better return-on-investments, by as much as three times.

ADI offers its vibration and shock sensors in ceramic packages, available in 70g, 250g, and 500g ranges.

High Accuracy Digital Temperature Sensor

Analog Devices is offering a high accuracy digital temperature sensor that covers a wide industrial range. The tiny package also incorporates a humidity sensor. There is no necessity of adding a separate analog to digital converter to this sensor, as the device has one built into it, and provides a high-resolution digital output of 16 bits. With a wide operating voltage range, the device is suitable for industrial, domestic, and commercial use.

The ADT7420UCPZ-R2 from Analog Devices measures temperatures from -40°C to +150°C, while operating from a voltage range of 2.7 to 5.5 V. The device is available in a 4 mm x 4 mm package commonly known as Lead Frame Chip Scale Package (LFCSP). This wire bond plastic encapsulated near chip scale package has a substrate of copper lead frame within a leadless package format. Input/output copper pads are positioned on the perimeter edges of the package.

This allows the user to solder the perimeter pads and the exposed paddle available on the bottom surface of the package to the PCB. The exposed thermal pad on the bottom of the package conducts heat away from the package when it is soldered to the copper layer on the PCB. The thermal and perimeter pads are tin plated to provide good soldering.

Within the ADT7420 is an internal band gap reference, along with a temperature sensor. The 16-bit ADC within the device monitors the temperature and digitizes it to a resolution of 0.0078°C. By default, the ADC resolution is set to 13 bits or 0.0625°C, which should be adequate for most users. However, the user can change the ADC resolution via a programmable mode, to 16 bits. The programmable mode is accessible to the user through an I2C serial interface.

Analog Devices guarantees the ADT7420 will operate reliably when supplied from 2.7 V to 5.5 V. Typical current consumption by the device id 210 µA when operating from a supply voltage of 3.3 V. The user can optionally power down the device to make it enter a shutdown mode where the current consumption is typically 2.0 µA at 3.3 V. There is an additional power saving mode, where the user programs the device to read one sample per second. The temperature drift for ADT7420 is merely 0.0073°C.

The ADT7420 exhibits very high temperature accuracy of ±0.20°C between -10°C and +85°C, when working from a 3.0 V supply. When working from a wider supply voltage of 2.7 to 3.3V, the temperature accuracy of the device is ±0.25°C between -20°C and +105°C. As soon as the device powers up, the first temperature reading is available within 6 ms.

Implementing the ADT7420 is very easy, as it does not need any temperature calibration or correction by the user. The user also does not require any linearity correction for the usable temperature range. The user can program the device to produce an interrupt when it senses the temperature crossing a preset critical temperature.

Applications for the ADT7420 include replacement for RTD and thermistor, and compensation for thermocouple cold junction. Typically, the device is usable in medical equipment, and for industrial control and test, food transport and storage, environmental monitoring and HVAC, and Laser diode temperature control applications.

Tree-Axis High Resolution Digital Accelerometer

Most modern smartphones can sense whether their users are holding them in the portrait or in the landscape position, accordingly adjusting the displayed image. Additionally, while playing games such as Temple Run, the smartphone can respond to tilting by changing certain functions in the game. The smartphone accomplishes this motion sensing as it has an accelerometer IC working inside it.

Apart from smartphones, several other applications make use of accelerometers. For instance, car alarms can be programmed to alert their drivers as soon as they cross a certain speed threshold. Hill Start Aid (HSA) systems depend on accelerometers to alert drivers when their vehicles start climbing a defined slope. Accelerometers tell weighing machines whether a vehicle is properly positioned before starting to take readings. Black boxes or data recorders in airplanes, trains, and other vehicles stop recording when an accelerometer decides there has been a violent incident.

Analog Devices makes ADXL313, one of such versatile digital accelerometers. The device has very high resolution of 13 bits on each of its three axes, and is capable of measuring up to ±4 g, where 1 g is the normal level of acceleration due to gravity at sea level. ASXL313 offers a 16-bit data output in a two’s complement format. The user can access this digital output through either an I2C serial interface, or a 3- or 4-wire serial port interface (SPI).

Being very small, only 5x5x1.45 mm, ADXL313 comes in a lead-free, RoHS compliant, LFCSP package and is qualified for automotive applications with a wide operating temperature range of -40°C to +105°C. The device is capable of surviving shocks up to 10,000 g. ADXL313 can work with a wide supply range of 2.0 to 3.6 V, consuming ultra-low levels of power. At a supply voltage of 3.3 V, the ADXL313 consumes only 30 µA in measurement mode, and only 0.1 µA in its standby mode.

While its embedded FIFO technology minimizes processor load for the host, ADXL313 offers an exemplary noise performance of typically 150 µg/√Hz for its X- and Y-axes, and typically 250 µg/√Hz for its Z-axis. While its user-selectable resolution is limited to a 10-bit resolution for any g value on the low side, its sensitivity is a minimum of 1024 LSB/g for any g range. On the upper side, its resolution scales from 10-bits at ±0.5 g to 13-bits at ±4 g. ADXL313 features a built-in motion detection function for monitoring activity/inactivity.

The ADXL313 3-axis digital accelerometer offers its user several flexible interrupt modes, which the user can map to two interrupt pins. Along with the built-in sensing function, the device can sense the presence or absence of motion, and detect whether the acceleration on any axis is exceeding the user-set level. The user can map these functions on two interrupt output pins, which can alert the controlling micro-controller accordingly.

ADXL313 has an integrated 32-level FIFO register to store data. This minimizes host processor intervention leading to a huge reduction is system power consumption. This low power mode enables intelligent motion-based power management and empowers the device with threshold sensing and active measurements while dissipating extremely low levels of power.

Accurate Power Monitoring with LTC2992

Linear Technology Corporation, now a part of Analog Devices, Inc., has recently placed on the market a power monitoring IC, LTC2992, which offers a wide-range, dual monitoring system for current, voltage, and power for 0-100 VDC rails. The IC is self-contained and does not need additional circuitry for functioning.

Users get a variety of options for operating the LTC2992. For instance, they can derive power from a 3-100 VDC monitored supply, or from a 2.7-100 VDC secondary supply, or from the shunt regulator on-board. Therefore, when monitoring the 0-100 VDC rail, the designer does not have to provide a separate buck regulator, a shunt regulator, or an inefficient resistive divider.

Within the LTC2992 are a multiplier and three Analog to Digital Converters (ADCs) of the delta-sigma type. Two of the ADCs provide measurements for current in each supply, while the third ADC measures voltage in 8- or 12-bit resolution and power in 24-bit resolution. The wide operating range of the LTC2992 makes it an ideal IC for several applications such as blade servers, advanced mezzanine cards, and 48 V telecom equipment.

Users with equipment using negative supply or supply greater than 100 VDC can make use of the onboard shunt regulator. The LTC2992 has registers that one can access with the I2C bus, and it uses these registers to store the measured values. It can measure current and voltage on-demand or continuously, using these to calculate the power, and stores this information along with maximum and minimum values in the registers.

The LTC2992 has four GPIO pins, which the user can configure as ADC inputs for measuring neighboring auxiliary voltages. Over its entire temperature range, the LTC2992 takes measurements with only ±0.3% of the Total Unadjusted Error (TUE). For any parameter going beyond the thresholds programmed by the user, the LTC2992 raises an alert flag in the specified register and on the specified pin. This is according to the alert response protocol of the SMBus.

The I2C bus on the LTC2992 operates at 400 kHz and features nine device addresses, a reset timer for a stuck bus, and a split SDA pin for simplifying the opto-isolation for the I2C. Another version of the IC, the LTC2992-1 offers users an inverted data output pin for the I2C. This makes it easy for the users to interface the IC where the opto-isolator has an inverting configuration.

The ICs, LTC2992 and LTC2992-1, are both available in automotive, industrial, and commercial versions. Their operating temperature ranges are -40°C to 125°C for automotive, -40°C to 85°C for industrial, and 0°C to 70°C for commercial applications. Linear Technology Corporation makes both versions of the IC in packages of 16-lead MSOP and 16-lead 4 x 3 mm DFN, and both versions are RoHS-compliant.

Most electronic applications require monitoring of current, voltage, and power at board level. Knowing the key system parameters provides valuable feedback, allowing users to monitor the health of their systems and make intelligent decisions. They help in determining whether a system is operating properly, efficiently, or even dangerously. Users can choose for various types of monitoring ICs, ranging from hot-swap dedicated power ICs to temperature monitors.