ELEKTOR AVRIL 2010 PDF

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Usually you can tell how much energy your heating system has consumed by checking your utilities bill, but what if you want elektof know how much heat it actually delivered? It also has a built-in control function for the circulation pump, which helps you reduce your environmental impact and keep your bank balance healthy.

Heating bills often present unpleasant surprises. Despite your best efforts to economise on heating, they list tidy sums for electricity or gas consumption. In this article we 20100 a relatively easy way to check these values and monitor your consumption almost continuously. All you need in order to determine how much heat your system delivers is four temperature sensors, a bit of wiring, and a microcontroller. The power Pwhich is amount of energy transferred per unit elektot, is:.

This value can be calculated directly from the flow velocity v of the medium and the inner diameter r of the pipe. This yields the formula:.

The temperatures can easily be rlektor with suitable sensors. Flow transducers are available for measuring the flow velocity, but installing a flow transducer always requires drilling a hole in a pipe or opening up the piping to insert a fitting. Measuring principle Here we used avrul different method to determine the flow velocity.

We make use of the fact that the supply and return temperatures always vary by at least one to two degrees due to the operation of the control system. If pairs of temperature sensors separated by a few metres are mounted on the elektpr and return lines, the flow velocity can be determined from the time offset of the variations measured by the two sensors.

As the water flows through the pipe with a speed of only a few elektoor per second, the temperature at sensor position S2 rises somewhat later than the temperature at sensor position S, which is closer to the boiler. An ATmega microcontroller constantly acquires temperature elektof from the two sensors. The time delay between the signals from a pair of sensors is determined by a correlation algorithm in the signal processing software, which shifts the signal waveforms from the two supply line sensors relative to each other until they virtually overlap.

The temperature signals from the sensors on eleltor return line are correlated in the same manner, and ideally the time offsets obtained for the supply and return lines should be the same.

To increase the sensitivity of the system, the return line sensor signals are applied to the inputs of a differential amplifier, and the resulting difference signal is amplified. This difference signal is also logged as a function of time. The area under the curve of the difference signal is a measure of the time offset of the temperature variations.

The accuracy of the measurements can be improved by applying some thermal paste between the sensor and the heating pipe. When you relocate, the system can be removed without leaving any traces behind. Hot water please If the heating system is also used to supply hot water for domestic use, additional pipes are used for this purpose.

For this reason, the PCB designed by the author includes inputs for additional temperature sensors. It also has a switched output for driving a relay that can control a circulation pump.

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Under certain conditions, eldktor the circulation pump can aril you a lot of money and significantly reduce CO 2 emissions.

This is because some systems have constant 20110 water circulation so users can draw hot water from the tap immediately.

This elekto electricity to power the pump, and energy is also lost through the pipe walls. This is detected by the temperature difference between the hot water and cold water supply lines.

It is important to ensure that there are no active branches between sensors S and S2 on the supply line or between sensors R and R2 on the return line. By contrast, three-way valves between the two sensor locations are not a problem as long as they are closed while measurements are being made.

It starts at the temperature sensors connected to the circuit board, which are NTC silicon devices. Their resistance varies by around 0. For example, the resistance of a KT sensor is approximately 1. The sensor for supply temperature S forms a voltage divider with resistor R This is followed by a simple low-pass filter formed by R36 and C20, which filters out induced Elekhor hum.

U4a amplifies the sensor signal by a factor of approximately 8. The TL used here is a rail-to-rail opamp, so the output voltage can assume almost any value within the supply voltage range. This increases the absolute measurement accuracy, since the full output signal amplitude is used. U4a naturally needs a reference voltage on its inverting input. This is provided by the combination of R20, R26 and R U5b acts as an impedance converter to minimise the load on the voltage divider.

The input stages for the other temperature sensors have a similar structure. The reference voltage for the sixth sensor, which is attached to the cold domestic water line cold-cold, CCis somewhat lower and is buffered by U5a. Consequently, the supply voltage does not require elaborate stabilisation.

If you want to know more about factors that may affect the measurement accuracy, you will find a worksheet in the download file for this project. The R and R2 sensor signals are also applied to the inputs of a differential amplifier built around U7a, and the resulting difference signal is amplified by a factor of Opamp U7d is wired as a comparator and triggers an interrupt in the ATmega microcontroller via pin PB1 when the supply line temperature rises.

Here C28 and R61 form a high-pass filter that more or less allows only changes in the signal level to pass. R47 is necessary to stabilise U4a with a capacitive load.

Schottky diode D9 prevents unallowable negative input levels on U7d when the circuit is not connected to a power source. U6a and U6b are also wired as elsktor for signals from the temperature sensors for hot and cold domestic water. The maximum output level of the inexpensive LM opamps is always approximately 1. These two opamps can pull port pin PD7 or PB0 respectively to approximately 0. Internal pull-up elketor in the microcontroller generate the high level. This means that the ATmega can spend most of its time in power-down mode.

This is also beneficial in terms of EMC because the clock is stopped in this mode. The bistable relay K1 is driven by T1 and T2. It is rated for only relatively low voltages and currents. If you want to switch a circulation pump, you will need a suitable power relay or contactor, which in turn is driven by K1. In case of circuits connected to the AC powerline, the usual safety regulations must be observed.

Never allow this circuit to come in direct contact with the AC power voltage. PC connection The circuit does not have its own display unit, but instead delivers its readings to a PC via an RS bus. Its functions can also be controlled from the PC.

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Free Elektor magazine April 2010

Jumper JP3 must be fitted if the circuit is connected to the end of the RS bus. The advantages of the RS bus system are its robustness and immunity to interference.

JP4 has yet another function: Always use headers with gold-plated contacts for the sensor connections, as otherwise the circuit will do elekyor good job of measuring any significant mechanical vibration. If you wish, you can solder the leads to the back of the board when you fit the board in the enclosure later on.

If you fit the board in the enclosure so the LED and the trimpots are visible or accessible through elekhor in the front, there will be enough room at the rear for the sensor cables. The best technique for soldering the leads of the sensor cables is to clamp the cable somewhere and use tweezers to position the pre-tinned ends of the leads. The next task is to load the boot loader software into the microcontroller via the ISP port.

The boot loader can be downloaded from the Elektor website [2] ; alternatively, you can purchase a pre-programmed microcontroller from the Elektor Shop.

Pololu – Free Elektor magazine April

After this the LED should start blinking. Reprogramming a few fuses is necessary to enable the boot loader to work properly, but first you should study the microcontroller data sheet carefully. Up to now the author has always had good results with programming the fuses individually and in sequence.

This way you can see exactly which function is involved if a problem arises. Next connect a RS adapter to the two middle pins of four-way connector P Naturally, the corresponding driver must also be installed on the PC before you can use the adapter. The next step is to launch the PC program termgui. If the Verify and Write buttons are not active after you press the Bootload button on the Maintenance tab, swap the two lines of the RS bus. The author wrote the software for the ATmegaAU boot loader and application program in C, and the source text can also be downloaded.

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After the sensors have been connected to the board, the initial temperature curves as yet uncalibrated should appear in the PC program. Alignment and calibration The first task is to adjust the three trimpots that set the voltage thresholds for interrupt trigging. During this process the temperature of the heating system supply line should remain constant and no domestic water should be drawn from the taps.

The LED is lit constantly when an interrupt pin is active; otherwise it blinks or is dark. The LED should go dark after 5 seconds. Next rotate each of the trimpots in turn fully in the opposite direction; the LED should light up. Then rotate the trimpot back in the other direction until the LED starts blinking or goes dark. A voltmeter connected to the input pins of U6a, U6b or U7d respectively is also helpful. Use the PC software to calibrate the temperature sensors. A software user guide with a brief description of the method is available in the Zip file that can be downloaded below.

If you wish to modify or extend the PC software, you will also find the source code and information on recompiling the code in the download. TV Elektor Ethics Back to top. Heating System Monitor Published in issueDecember Follow project Add a comment.