"Not long ago, aiban.com got a digital thermometer hh11b launched by Omega company. Omega company is a precision instrument manufacturer with a history of more than 50 years and focuses on process measurement and control. It has more than 100000 products for measuring and controlling temperature, humidity, pressure, stress, flow, liquid level, pH and conductivity, At the same time, it provides customers with complete data acquisition, electric heating and customized design products, and hh11b is a portable economic digital thermometer of Omega company, which is one of the common contact thermometers.
At present, the commonly used contact thermometers can be roughly divided into thermal resistance and thermocouple. Thermal resistance measures temperature based on the characteristic that the resistance value of conductor or semiconductor changes with temperature. The measurement accuracy is high, but the temperature measurement range is relatively small, which is mostly used for medium and low temperature measurement; The thermocouple thermometer is different. The two ends of two conductors with different components are connected to form a circuit. When the temperatures of the two junction points are different, electromotive force will be generated in the circuit. Using this electromotive force for temperature measurement, thermocouple temperature measurement is rapid and has a wide temperature measurement range. It is a product with a wider application range than thermal resistance. The hh11b of Omega is a digital thermometer based on the principle of K-type thermocouple (the principle of K-type thermocouple can be evaluated with reference to the 16 bit ADC Ti ads1118 evaluation board with the smallest area).
Digital thermometer hh11b
The hh11b thermometer obtained by aibanwang includes a temperature measuring main machine and a K-type thermocouple (see the figure below). Hh11b doesn't look so small. Its circumference is about 210mm * 65mm * 33mm, which is larger and thicker than ordinary TV remote controls. However, the streamlined design makes it very comfortable to hold. In addition, the whole hh11b thermometer has about 254g, which is equivalent to the weight of more than two iphone5s. It is very stable in your hand.
Digital thermometer hh11b and type K thermocouple
Hh11b specific parameters:
Measuring range: - 200 ~ 1372°C (-328 ~ 1999°F), -199.9 ~ 199.9°C (-327.8 ~ 391.8°F)
Accuracy (K-type chrome aluminum): - ± at 60 ~ 1372 ° (0.1% + 1 ° C of reading)
-± at 60 ~ 200 ° (0.1% + 2 ° C of reading)
-± at 76 ~ 1999 ° (0.1% + 2 ° F of reading)
-± at 76 ~ 328 ° (0.1% + 4 ° F of reading)
Temperature coefficient: 0.1 times the relevant accuracy specification per ° C between 0 ~ 18 ° C and 28 ~ 50 ° C
display: 3-bit and a half LCD with a maximum reading of 1999
Sampling rate: 2.5/s
Battery: 9V (included)
Battery life: Usually 200 hours
From the parameters of hh11b digital thermometer, we can see that through the selection of different K-type thermocouples, we can carry out temperature tests in different ranges, and the measured temperature value may have different degrees of deviation due to the selection of different K-type thermocouples, but the error range can be judged by the simple calculation formula above. Similarly, it depends on the 3-bit and half LCD of hh11b, The highest bit of LCD can only display 0 or 1, so the maximum range we can measure is 1999, but it is more than enough for general occasions.
The front main control panel of hh11b is very simple. From top to bottom, it is a segment LCD, an LED for detecting the open circuit of K-type galvanic couple, five function keys and a temperature calibration knob. The back is more simple, with a simple instructions and a battery compartment that can replace the battery.
Digital thermometer hh11b front and rear panels
HH11B's simple appearance makes it easy to feel that the operation is very simple. Although it is true, it still takes a lot of effort to first use and no one guides. It is a question that there is no Chinese instruction in Chinese mainland Chinese sales. Here is a brief introduction to the functions of the next few buttons (except ON/OFF):
Min / Max: this key can record the minimum, maximum and average temperature changes from the moment of pressing
Hold: lock the current temperature value
Rel: press this key, the temperature display will be cleared, and then the relative value of the temperature change at the time of pressing will be displayed
Apo > 2S ℃ / ° F: set the unit of temperature display that can be switched off automatically without power supply for a long time and long press for 2S - Celsius / Fahrenheit
Offset: K-type thermocouple can be placed in ice water mixture (0 ℃) to calibrate the temperature
The functions of these keys can exit the entered functions by long pressing the corresponding keys (apo > 2S ℃ / ° f is not used). These functions of hh11b are very common and practical, and are competent in general occasions. Without prior calibration, the author also tried hh11b and tested the temperature of ice in the refrigerator. The measured value has been hovering around 3 ℃. Aside from the error, it is also a little different from the actual temperature. It seems that this thing must be calibrated before use (offset button), otherwise it will not pit you.
I've seen and used it. The comprehensive evaluation of the appearance and function of the digital thermometer hh11b of Omega company is quite OK. There are no particularly obvious shortcomings. The workmanship and material are excellent, which makes the author better wonder its internal structure and must be disassembled to see what happened.
Disassemble hh11b
Just like the simple appearance design of hh11b, the structure of hh11b is also simple. It takes no effort to disassemble hh11b. Unscrew the screws in the back battery compartment to see the 9V powered battery. Continue to unscrew the remaining four screws and take off the back cover to see the real appearance of hh11b.
Disassemble hh11b back housing
From the first glance, we can roughly judge that the circuit design of hh11b is very simple. It basically depends on a microcontroller chip. In fact, it is only a function of temperature measurement after all. The function is simple to realize, but we need to make real efforts to ensure the accuracy of temperature measurement. We ignore these first and continue to disassemble other parts.
Hh11b is completely disassembled
Disassembly is basically not difficult, structural reorganization is also very convenient, and things are not many and complex. Even if it is broken, it is easy to repair. From the perspective of a product, this is undoubtedly a successful work. To some extent, the product designer did it with his heart. The internal and external workmanship is consistent. It is not as golden as Baidu wireless music box, another product disassembled by the author before. OK, let's take a closer look at each part.
Microcontroller fs98o22
The circuit composition of digital thermometer hh11b is not complex. It is mainly a single-chip solution based on crystal rich electronic microcontroller fs98o22. Fujing electronics is a well-known semiconductor enterprise in Taiwan. Founded in 1995, Fujing electronics is committed to the measurement technology solution of single chip, which is indisputable first in Asia (because no one competes). Although there is still a certain gap compared with the measurement technology in Europe and America, the price factor makes it competitive. Among similar products, the price is lower than 2 / 3 of that in Europe and America.
Microcontroller fs98o22
As a highly integrated mixed signal processing single-chip OTP microcontroller in fs98xx series released by Fujing in 2004, fs98o22 integrates LCD driver, low-noise operational amplifier and digital to analog converter (see the system block diagram of fs98o22 below). It has unparalleled advantages in fields requiring single-chip solutions such as electronic scales and sensors, greatly reducing the difficulty of circuit design, Reduce peripheral devices and reduce material cost.
Fs98o22 system block diagram
But at the same time, the accompanying problems also come. As the author said, fs98o22 is a product in 2004. While admiring its long life cycle, I have to praise its reliability. Of course, the two are interdependent, but I have too much hope for its performance. After all, it is an antique chip. See the main characteristics:
The 8-bit CMOS reduced instruction set microprocessor integrates 8KB OTP ROM and 256 bytesram, with only 37 instructions
Working voltage: 2.2V ~ 3.6V, 4 * 20lcd drive
8-channel 14 bit ADC, a low noise operational amplifier
Less than 3mA in working mode and about 3ua in sleep mode
It is worth affirming that this is a microcontroller independently developed by Fujing electronics. Although these parameters are at the bottom of today's single chip microcomputer ranks, it is difficult to see such antique things after seeing the arm core Microcontrollers in the "rotten Street". Moreover, it is estimated that fs98o22 has great advantages in price. In product design, it is good to choose the design scheme. On the premise of ensuring enough, cost saving is the goal that every company spared no effort to pursue, which may also be an important factor for Omega to choose it as the product scheme at the beginning.
Looking at the nominal power consumption of fs98o22, it is less than 3mA in working mode and about 3ua in sleep mode. Maybe it can be regarded as low power consumption at that time, but in today's era, not to mention ti's MSP430, ATMEL's sam4l series (based on ARM cortex M4 kernel) have lower power consumption than it, let alone performance. The most real portrayal of microcontroller fs98o22 today is the age of heroes.
Of course, this does not mean that fs98o22 has no advantages. The most important function of hh11b thermometer, temperature conversion function, is mainly completed by ADC. As previously introduced, crystal rich electronics still has certain authority in the field of measurement and simulation. Therefore, even the products of 2004 are not bad in terms of ADC. The 8-channel 14bit full differential ADC is enough to surpass Ti MSP430, However, this comparison may seem extreme and unfair. It is inevitably suspected of developing strengths and avoiding weaknesses. If we really want to compare with products that also sell ADC, such as TI's new ads1118 chip (which is also a low-end product and is similar to the field), the ADC performance of fs98o22 seems weak. Therefore, according to the current situation, fs98o22 is in a very embarrassing situation, In addition to the advantage of price in single-chip solutions, the author really can't think of anything else.
Let's look at other parts of the PCB. Next to the fs98o22 is the filter circuit at the input of the ADC, which is connected with a K-type thermocouple. The other 8-pin IC below is the EEPROM of Italy France semiconductor. The whole board is powered by a 9V battery to a 3.6V voltage to the microcontroller.
Interesting "connector" for segmented LCD
Flip the board card, and there are fewer circuits on the other side. Except for a segmented LCD module and several function keys (the black knob is the rheostat for calibrating the temperature), there is nothing. What is interesting is the connection mode between the segmented LCD module and the PCB board.
Connection mode between Segment LCD and PCB
Accustomed to the usual LCD connector or FPC welding connection, the LCD interface of hh11b shines in front of people. Two rubber? No, fools know that rubber cannot conduct electricity. How can it replace the role of wires?
The black-and-white thing on the back of the LCD screen is called "silica gel zebra strip", that is, conductive silica gel. At first glance, it may be very novel and interesting, but once you figure it out, you can understand it. In fact, it is also a very common "connector", such as the physical button of the handset and the remote control of the TV at home, The point where the hard key or soft key contacts the PCB circuit board is generally made of conductive silica gel, such as the black circle on the function key measured on the left in the figure above.
However, another problem that follows is how to ensure that the conductive silica gel interface of LCD can realize pin to pin with the metal contact of PCB. If it is misaligned, it is easy to cause short circuit and burn the board and card. Here we should praise the structural design of hh11b. A plastic screen card cover and the structural fixation of the front panel completely avoid this problem during assembly, Take it apart and reassemble it without worry. In some product designs that pursue simplicity and convenience and require cost reduction, conductive silica gel can be considered as a "connector".
K-type thermocouple socket
Finally, let's take a look at the plug-in base of K-type thermocouple, which is relatively simple, A warning sign can be seen at the interface of hh11b external K-type thermocouple: the maximum DC voltage is 60V and the maximum AC voltage is 24V. It is mainly connected to the main board through a 4Pin pin socket (see the figure below).
K-type thermocouple socket
The triode next to the K-type thermocouple interface on the small board above and the knob variable resistance mentioned earlier constitute the hardware circuit of hh11b digital thermometer temperature calibration function. In the whole product design, considering the plug-in mode of K-type thermocouple, hh11b is designed into a control motherboard and a small board structure. Otherwise, a main PCB can handle all functions.
Finally, after disassembly and analysis, we can basically understand the hardware principle block diagram (see the figure below)
Hardware block diagram of digital thermometer hh11b
The principle of digital thermometer is very simple. I believe netizens with design basis in this regard can learn from and choose better solutions, such as Ti ads1118 chip and DIY, a more cost-effective digital thermometer product. Of course, the author does not deny Omega's excellent product design on hh11b digital thermometer. Although the selected hardware scheme is general, the product details are very in place, there are no particularly obvious defects, and the reliability is greatly guaranteed. I believe it will still be favored by some people.
After reading the disassembly, I believe you know well about hh11b digital thermometer. The selling price of Omega's official website is 560rmb, which is not much different from that of similar products of other European and American brands. Of course, compared with some domestic thermometer products, hh11b is slightly high-grade. Consumers who have high requirements for product details or are interested in Omega can buy one to see if it is worth it“
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