During firing bricks, the brick moisture is a parameter that needs to be strictly controlled. According to process requirements, the brick water should be controlled between 14% and 14.5%. At present, it is typically detected according to the drying method, so that the field brick billet is sampled, and the weight of the mud brick is calculated after the sample removal of moisture after drying. This detection means is high, but the cycle is too long, and it is generally required to get the test results. This article introduces a simple circuit, easy, easy to use, easy to use, and high test and high accuracy, it is particularly suitable for on-site measurement and sampling. I. Working principle This tester is measured according to the principle of the resistance value is also changed according to the change in the water content of the brick. It can distinguish 0.1% of the water content change. At the same time, since the measurement section is controlled, its accuracy can achieve a higher degree. The principle of electricity is shown in Figure 1.
The water content sensing signal is obtained from the detection probe inserted into the brick. The larger the water content, the smaller the resistance between the probe; the smaller the water content, the larger the probe resistance, the change in the probe resistance corresponds to the change in the water content of the brick. In Figure 1, the core component is used to drive 10-bit LEDs LM3914 (domestic model SF3914, Shanghai Radio Seven Products), and the LM3914 has the characteristics of the LED display bits and its input voltage into good linear relationship. The internal circuit is shown in Figure 2. There are 10 voltage comparators inside the LM3914, with 4, 6 floating ten high-precision voltage divider, which also has a floating DC voltage reference source, input buffer and display mode selection amplifier and other circuits. The reference voltage 7, the voltage is 1.25V, so the voltage division of 125 mV, 250 mV ... 1250 mV can be obtained in the same phase end of the comparator. The reference voltage source can provide a current of 3 to 4 mA, and the driving current of each LED is substantially 10 times that of the reference voltage source output current, that is, the drive current ILED = 10 × 1.25 / r5 of each LED in Fig. 1 (MA) ).
The LM3914 also has a point / line display selection function. When its pin is connected to 11 foot, select the point diagram display, there is only a bit number of the LED display, and the serial number value corresponds to the size of the input voltage. When the LM3914 is connected to the VCC terminal, select the line diagram display function, there is a number of bit LEDs display, and the number of LEDs is corresponding to the input voltage. In order to improve the measurement resolution, the circuit of Figure 1 uses a method of sub-test. Since the amount of brick moisture and its resistance change are not strict, it has a large nonlinear, and the distribution test is conducive to improving linearity and improving accuracy. In the drawing of the LM3914 internal reference voltage source UREF (1.25V) by the R1-R4, the in-phase input as the op amp A1, according to its division value, can determine the water content measurement area, so adjust K1 can select the measurement area. For example, when the switch K1 points to "14%", the selected water content measurement area is 14% to 15%. Figure 1 The circuit is 13% -16% in the total measuring area of 13% to 16% depending on the actual needs of the brick equipment. The measurement process can be analyzed: assuming that K1 points 14%, the A1 output voltage U01 is output in the circuit. When the water content of the brick is 14% is equal to zero. When the water content of the brick blank is 14% + 0.1x%, A1, A2 is proportionally converted, so that the LM3914 drives X LED display (or the X-bit LED display), so the water content of the brick blank is equal to LM3914 drive The thousandth of the LED display value plus 14%, which can also be launched, when K1 points to other files, the measured value is equal to the number of gear display values plus the LED display value. Thus, by the gear switch, the circuit can always distinguish between 0.1% in the measurement range of 13% -16% measurement range. Figure 1 switch K2 is a point / line conversion switch, and the LED implementation point diagram display or line diagram display can be displayed as needed. Second, debugging and making commissioning can dry the results measured by the experimental method as the standard value, adjust the respective voltage resistance values (R1 to R4) to satisfy the circuit measurement accuracy. Here, the debugging step is as follows: First, the switch K1 knife is located at the "13%" gear, insert the sensor probe into a mud brick in which the water content is 3%, and the small range adjusts the R1 value. The A1 output voltage is zero, and then insert the probe into a mud brick in which the water content is 14%, adjusting the R6 or R7 value, so that the 10-bit LED of the LM3914 is just displayed, and the measured value is 14%, R6 or R7. After adjusting, the debugging of each file can be adjusted without adjustment. Finally, according to the above steps, adjust each file, adjust the respective partial pressure resistance, and make the measurement of water accuracy satisfy the requirements. In order to achieve high accuracy measurement, each resistor element should use a good stability of metal film resistance or wire resistance. Figure 1 The circuit selected precision op amp07, if the requirements are not very high, optional one LM358 dual op amp. In order to make the circuit work normally, it should be powered by ± 5V dual power supply. LED display brightness is determined by R5, and the R5 value is 1 to 2.7kΩ. The sensor probe is made with colloidal wood and stainless steel, and the shape size is shown in Figure 3. Since the insertion depth of the sensing probe has a certain impact on the test (maximum impact more than 0.5%), the depth of each test process probe should be guaranteed. Due to the mud brick temperature, texture and its impurities have a certain effect on the measurement results (such as the scriptures test, the temperature is 10 ° C, the absolute indication error increases by about 0.15%), so it is actually used this brick hydraulic tester. Smallest range status should also be performed. In order to eliminate the impact of the ingredients of the mud bricks on the test results, the average measures should be taken from multiple measurements.
Our other product:
