Regularly Smartec is asked for a temperature sensor with an I2C output. Because of the low power consumption of the SMT172 sensor itself, the self heating of the sensor is negligible, which contributes to its precision. An on chip integrated I2C interface would produce too much heat. The only way to preserve the sensors precision and still have an I2C interface, is to combine them on a tiny pcb. This board also does the calculations on the sampled duty-cycle and converts the result in ASCII data with an accuracy in the range of mK.
The board can be used in PWM mode (instead of I2C mode), to meet compatibility requirements with some existing (obsolete) SMT160-30 applications.
Accurate measurement in full SMT172 temperature range
Measures the output of the SMT172 in 0.001 °C steps
Both I2C and PWM (SMT16030 like) output
Board temperature range 0 – 75 °C
Programmable secondary address, allowing for multiple sensors with interfaces on the same I2C bus
3.3 V. regulator for powering the SMT172
Powered by the I2C bus itself
Can be used for all housings of the SMT172View or download SMT172TOIIC.pdf , click here.
We have developed a few modules that make designer’s lives easier and show off the great features of our sensors. Some of these boards are being used in measurement and production environments due to their ease of installation and the high quality of the outputs.
For the temperature sensors we offer the SMTAS04 and SMTAS08 boards. These boards can be connected to any PC using a USB cable – no extra power supply needed! These boards have high accuracy and great resolution (0.01C).
We have also developed a new UTI evaluation board; the UTI Evaluation Kit USB. This board is a real “plug and play” system. Very accurate capacitance and resistance values can be measured. Porting the very low output voltages of infrared sensors to other equipment is very challenging so we have designed an IIC interface module and USB module that make this very easy.
The Smartec humidity sensor is a two terminal capacitor, which increases in value as water molecules are absorbed into its active polymer dielectric. The capacitor plates consist of a base plate and a water permeable platinum top plate.
The measuring of humidity is rather complex. Generally the humidity in air is measured as the fraction of the maximum amount of water that can be absorbed at a certain temperature. In air, at a given temperature, this fraction can vary between 0 (absolute dry) and 100 % (the point where condensation will begin to form).
Many classical sensing techniques, such as mechanical devices and resistive type sensors, are temperature dependent and the wet bulb thermometer is pressure dependent. With the SMARTEC Humidity sensor RH can be measured without the complicating factor of temperature and pressure. To protect the sensitive layer of the sensor in the first quarter of 2010 a special encapsulation will be available.
The Smart Pressure Device SPD series of pressure sensors are silicon based and encapsulated in all kind of housings. The pressure range can vary between about 10 mBar and 20 Bar gauge and differential. In case of an absolute version the reference vacuum chamber is formed on the die during manufacturing. Due to fact that the bridge resistance values, the bridge output pressure sensor is especially suited to use in combination with the Universal Transducer Interface (UTI03).
The Smartec Pressure Devices are based on the principle of bending a membrane caused by the pressure in a liquid or gas. On the membrane is a very thin conductive screened layer that that follows the bending of this membrane. The resistance of the conductive layers will change when the membrane is bended. A smart mechanical layout of four resistive structures can form a stable Wheatstone bridge, comparable with the classical strain gauge sensors.
The bending of the membrane (and also the layer) is very small (<< 1 mm), but is still large enough to measure the changes in the resistive values. The resistive structures on the surfaces can be compressed or stretched depending what direction the membrane is bended. When the layer is compressed the resistance value will decrease and when stretched this value will increase. In practice this means that the Wheatstone bridge is imbalanced in a positive and in a negative way respectively.
In general the screened resistors are also sensitive to temperature which means a compensation for temperature effects is required. For the Smartec pressure sensors this compensation is done in the amplifier to obtain a stable analogue output.
The Universal Transducer Interface (UTI) is a sensor-to-time signal converter, based on a self-calibrating period-modulated oscillator. Sensing elements can be directly connected to the UTI without the need for extra electronics to interface all different sensor type. The output is digital and can communicate with any type of micro-controllerThe Universal Transducer
Interface (UTI) is a sensor-to-time signal converter, based on a self-calibrating period-modulated oscillator. The UTI can operate in 16 different modes. To obtain accurate results in any of these modes a reference element of the same kind as the sensor is required.
The UTI provides interfacing for:
Capacitive sensors 0-2pF, 0-12pF, variable range up to 300pF
Platinum resistors Pt100, Pt1000
Thermistors 1 KOhm-25 KOhm at room temperature
Resistive bridges 250 Ohm-10 KOhm with maximum imbalance +/- 4% or +/- 0.25%
Potentiometers 1 KOhm-50 KOhm
In the exactly same way as the unknown sensor signal is measured, both a reference signal and an internal (constant) offset are measured during two additional phases. Continuous auto-calibration of offset and gain of the complete system is then achieved by processing these values (time signals) by microcontroller software. The output signal of the UTI is digital so compatible with any type micro-controller.
For convenience design-in there are evaluation boards available. In combination with the free downloadable software application will work in shortest time.
The multiplexer MUCC01 is especially designed for use in combination with the Smartec Universal Transducer Interface (UTI). The combination of the UTI and the MUXC01 makes it possible to measure multiple capacitances with a very low capacitance value and a very high accuracy (15 bits).
The multiplexer is special designed to combine with our UTI measuring very accurate capacitors.
By cascading the multiplexers it is easy to extend to the quantity of capacitors needed. Each multiplexer contains a 9 bits shift register and can handle 9 capacitors. Because the capacitance measurement is based on charge transport, special attention is given to the outputs of the circuit. By means of the design the multiplexer has an output impedance of less then 20 Ohms and also the rail-to-rail output voltage is well defined. These requirements make the combination of the UTI and the multiplexer the best solution to multiple capacitance measurement. By constructing array’s each possible capacitance structure can be measured easy and accurate. The device is available in DIL, SOIC or as bare die.
The Smartec infrared sensors SMTIR99XX are sophisticated full silicon infrared sensors and comprise of so called thermopiles. Thermopiles are based on the Seebeck effect, which is a long time standard for conventional thermocouples. The application of thin film technology allows the production of miniaturised and low cost sensor elements. For specific applications there is a version with a small openings angle (7°).
The sensors can be used in measuring the radiation temperature without any contact. For different radiation temperature ranges various filters are available. The sensor type SMTIR9902 contains a temperature sensor for measuring the temperature of the sensor itself. The temperature range of the sensor-element is between -40 to 100 °C. The sensor is available in a standard TO-05 encapsulation and is standard wise equipped with a 5.5 micrometer filter. For a small field of view there is an infrared sensor available with a silicon lens.
The output voltage is generated by a thermopile, formed by a series connection of thermojunctions deposited on a silicon substrate. The hot junctions are thermally isolated from the cold junctions on the substrate by etching an extremely thin membrane. A black absorbing layer on the hot junctions transform the incoming radiation into heat. A voltage proportional to the radiation is generated by the thermoelectric effect.
The used thermopiles are processed on silicon substrates using BiSb and NiCr for the thermojunctions. For different radiation spectra various filters are available to get the optimal solution.
Easy and accurate measuring of the sensor temperature can be done with a built-in temperature sensor (only for type SMTIR9902).
-Duty-cycle (PWM) output
-2.7 – 5.5 V power supply
–Analog voltage output with a low-pass filter
-Wide range of packaging possibilities
-Market proven excellent quality and stability
-Used in both:
High end market (medical and space industry) and
Low end market (consumer products)
The SMT172 is a three terminal integrated temperature sensor, with a duty-cycle output.
Two terminals are used for the power supply of 2.7 -5.5 Volts and the third terminal carries the output signal. A duty cycle modulated output is used because this output is interpretable by a microprocessor without A-D converter, while the analogue information is still available.
The sensors are available in a number of encapsulations: TO18, TO92, TO220, SOIC-8L, SOT223 and others. The temperature sensors are available as naked die as well. On request the sensors can also be built in customer specified encapsulations. For quick design-in a lot of application are available on the web and for plug and play we have designed Smart Temperature Acquisition System for 4 or 8 Smartec Temperature Sensors. It was designed to get the best possible temperature measurement results with the SMT172 Smartec temperature sensors (absolute accuracy 0.25 °C, noise <0.0004 °C), at little cost. With it, you don’t have to develop your own hardware application to connect 8 SMT172 temperature sensors to a PC. This board does it for you. On our website an application can be found to connect the board to an Excel or a simple labview application. In this way a low budget high accurate measurement system can be build.
The SMT172 has an overall accuracy of 0.1 °C in the range from -20 °C to +100 °C and an accuracy of 0.4 °C from -45 to +130 °C. This makes the sensor especially useful in all applications where “human” (climate control, food processing etc.) conditions are to be controlled.
The CMOS output of the sensor can handle cable length up to 20 meters. This makes the SMT172 very useful in remote sensing and control applications.