Omron D6T Series - User Manual

The Omron D6T MEMS Thermal Sensor is a sophisticated device designed for measuring the surface temperature of objects. It integrates a silicon lens, a thermopile sensor, and specialized analog and logic circuits on a small circuit board to convert thermal energy into a digital temperature value. This compact design, available in various sizes (e.g., 14 mm x 18 mm or 11.6 mm x 12 mm), requires only a single connector for system integration, simplifying its use in diverse applications.

Function Description

The core principle of operation involves the silicon lens focusing radiant heat (far-infrared rays) emitted from objects onto the thermopile sensor. The thermopile sensor then generates an electromotive force proportional to the focused radiant energy. This electromotive force, along with data from an internal thermal sensor, is used by the device to calculate the object's temperature through an interpolation process, comparing measured values with an internally stored lookup table. The resulting temperature value is output via the I2C bus, ready to be read by a host system.

The D6T series offers different channel configurations to suit various needs. For instance, the D6T-44L-06 model features 16 channels in a 4x4 arrangement, while the D6T-8L-09 has an 8-channel array. The D6T-1A-01 and D6T-1A-02 models are equipped with a single-channel sensor chip. The module's design optimizes the placement of the downstream processing circuit adjacent to the sensor chip, ensuring low-noise temperature measurements.

A key advantage of the MEMS Thermal Sensor over conventional pyroelectric sensors is its ability to continuously generate a measurement signal, even when there is no movement. Pyroelectric sensors detect movement based on changes in infrared rays, meaning their signal is lost during periods of stillness. This makes the D6T series particularly suitable for applications requiring constant presence detection, such as human sensing, without the limitations of motion-dependent sensors.

The silicon lens is optically designed to provide specific sensitivity characteristics. The sensors maintain a consistent field of view (FOV) at a maximum sensitivity of 50% compared to general sensors. It's important to note that the sensitive areas of the elements are wider than the FOV-specification width. If the measured object is smaller than the sensitive area of an element, the background temperature of other objects can influence the reading. The sensors use a reference heat source (a blackbody furnace) for temperature value correction, but factors like object emissivity, surface shape, and the occupancy ratio of objects within sensitive areas can still affect temperature values.

The measurable area (FOV) expands as the distance to the measured object increases. Consequently, the occupancy ratio of objects (e.g., people) within the FOV decreases with distance. This means that at greater distances, the temperature values become more representative of the background temperature rather than the intended object's temperature. For accurate temperature measurement of intended objects, the object must be sufficiently larger than the FOV area. When used as a human sensor, the D6T is primarily limited to close-distance applications for simple temperature value determination. To enhance detection distance and accuracy, software processing that incorporates temporal changes, heat source positions, and human behavior information is recommended.

Usage Features

The D6T MEMS Thermal Sensors are designed for straightforward integration into various systems. They utilize a 4-pin connector (SM04B-GHS-TB (JST) with SSHL-002T-P0.2 (JST) contacts and GHR-04V-S (JST) housing) for power supply and I2C communication. The VCC power supply pin operates at 5 V ±10%.

Several electrical connection scenarios are supported:

5 V MCU Direct Connection: For microcontrollers operating at the same 5 V supply voltage, a direct connection is possible, typically involving pull-up resistors on the SDA and SCL lines.
3 V MCU (I2C port is 5 V fault tolerant): If the microcontroller operates at 3 V but its I2C port is 5 V fault tolerant, the sensor can be connected directly, again with appropriate pull-up resistors.
Using an I2C Level Converter: For 3 V MCUs that are not 5 V fault tolerant, or when other devices are connected to the 3 V I2C bus, an I2C level converter (e.g., PCA9517) is used to bridge the voltage difference between the MCU and the 5 V sensor.
Using a Bidirectional Open-Drain GPIO Terminal: If the MCU lacks built-in I2C functionality, a bidirectional open-drain GPIO terminal can be used, with I2C communication processing handled in software. This scenario requires clock stretch support.
Using an I2C Bus-Switching IC: For connecting multiple D6T sensors, an I2C bus-switching IC can be employed. It's important to note that this sensor cannot change slave addresses, and most bus-switching ICs also offer power voltage conversion functionality.

The I2C communication specifications include a 7-bit slave address (0001_010b), 8-bit data length (MSB-first), and a maximum clock speed of 100 kHz (1000 kHz for D6T-32L only in Fast-Mode Plus). Clock stretch support is available for all models except D6T-1A-01, D6T-1A-02, and D6T-8L-09.

The sensor's output data includes PTAT (Proportional To Absolute Temperature) and Pn (pixel temperature) values, which are signed 16-bit integers representing temperature values in °C multiplied by a factor of 10. For example, 25.0°C is represented as 250 (0x00FA), and -25.0°C as -250 (0xFF06). The output data also includes a Packet Error Check (PEC) code, which is a CRC-8 error check data appended to the end of communication output. This PEC value allows users to detect communication errors and enhance data reliability.

For D6T-8L-09 models, an initial processing step is required at least 20 msec after power-on, which should only be performed once at power startup. Similarly, for the D6T-32L-01A, register settings can be changed, and this processing should also be performed at least 20 msec after power-on, only at power startup. The D6T-32L-01A allows setting an IIR filter coefficient (0 to 15) to adjust temperature averaging.

The D6T-1A-01/02 and D6T-8L-09 models do not feature clock stretch. For models that do, the slave (sensor) can generate a signal to the master (MCU) to request a wait period before sending a request, based on the temperature data state. The master MCU must support this wait processing. If the MCU's I2C module lacks automatic clock stretch support, a wait detection routine must be added to the SCL output portion of the program. Alternatively, a fixed 160 µsec wait time can be added at every Ack timing.

Communication timeouts are implemented to prevent indefinite waiting. If low input is continuously received on the SDA or SCL terminal for 1 second (D6T-44L-06) or 70 msec (D6T-1A-01/02/8L-09), the sensor determines a timeout has occurred and stops communication. During a Write access operation, a NACK is returned. For Read access operations, the read value is set to FFFFh. Using PEC for data checking is recommended to identify erroneous read values.

Maintenance Features

The D6T MEMS Thermal Sensor is designed for robust and reliable operation, but certain considerations are important for its long-term performance and integration:

Surface Cover Material: When installing the sensor as part of an assembly, the cover material must have sufficient radiant heat (far-infrared) transmissivity. High-density polyethylene (HDPE) is often used due to its cost-effectiveness and ease of molding. The rate of signal decay varies with cover thickness, so using the thinnest possible cover is recommended to minimize negative impact on detection performance. However, if the cover is too thin, the internal sensor may become visible.
Sensor Securement: The sensor should be installed so that it is enclosed by a casing and secured at designated mountable areas. Detailed diagrams are provided for D6T-44L-06, D6T-8L-09, D6T1A-01/-02, and D6T-32L-01A models, indicating the specific areas for securement.
Operational Stability: After power is supplied, output temperatures will be within the specified accuracy range within a few seconds. However, fully stable operation typically takes approximately 15 minutes.
Power Consumption: The D6T series of sensors is not configured with a "power-conserving sleep" operation mode. To reduce power consumption, the power to the sensor must be shut off when not in use.
Temperature Data Update Rate: For standard specifications, the sensor updates temperature data every 300 ms or less (250 ms or less for D6T-8L-09, and 100 ms or less for D6T-1A-01/02). This operation is independent of any communication processing, and temperature update timing cannot be controlled externally.
Firmware and Software: The provided example programs for temperature value retrieval and PEC check routines are configured with standard I2C operations library functions. Users are advised to replace these with similar functions available in the microcontroller used in their system when testing the program.
Troubleshooting: The manual includes a FAQ section addressing common questions, such as increasing the field of view (limited by silicon lens constraints), interference from infrared remote controllers (not an issue due to wavelength filtering), distinguishing between people, animals, and appliances (requires user-developed software), usable detection distance as a human sensor (approximately 5 to 6 m, depending on installation and algorithm), and power consumption reduction (requires shutting off power).

The D6T series is designed for reliability and ease of use, providing a robust solution for various thermal sensing applications with careful attention to integration and operational guidelines.

Omron D6T Series Specifications

General

Model Series	D6T
Detection Method	Non-contact
Interface	I2C
Output Type	Digital
Type	Thermal Sensor
Field of View	Varies by model
Number of Pixels	Varies by model
Operating Temperature	Varies by model
Storage Temperature	Varies by model
Response Time	Varies by model
Dimensions	Varies by model
Humidity Range	85% (non-condensing)