In the process of creating Amateur designs may require devices and the equipment, which is often difficult. In such cases, the aid comes wit, and craftsmen do their best with their hands. We will tell how to make a real chart recorder-temperature recorder from an old electrocardiograph type ACT-03M (Fig. 1).
This device may be required to measure and record temperature specific areas (parts) for some time. Explain with an example. Collecting a powerful computer with your hands, you may encounter a problem overheating of the processor. For cooling will require a cooling system, which obviously will eliminate the risk of failure of the "computer brain". Well, if you possess the appropriate method of calculation. And if not? You can, of course, immediately to turn on the computer and see - "burn" the CPU or not?
I doubt you PI will satisfy the sad outcome of this experiment... it is Much better to check the efficiency of the cooling system under model conditions, measuring the growth the temperature of the radiator, which will subsequently contact the processor. Using this model the heat source and the temperature recorder, you can easily to choose the design parameters under which the processor will be guaranteed from overheating.
Fig. 1. Appearance: 1 - button power on; 2 - off indicator network; 3 - a regulator of intensity pen; 4 - plug for connecting the cable leads; 5 - the switch of leads; 6 - control the displacement of the pen; 7 - button calibration; 8 - button switch speed; 9 - button-calm; 10 - record button; 11 - switch sensitivity
It is useful to mention the principle of self-made temperature recorder. In the technique well-known methods of temperature measurement with te thermometers (thermocouples). The thermocouple is a two-conductor of different material constituting the common electrical circuit (see Fig. 3). If the temperature of the joints (junctions) of the thermocouple varies, then there is the thermal voltage and the circuit current flows. The thermo-EMF is greater, the greater the difference temperatures of the junctions. Connecting the thermocouple with recorder, obtain the device, allows to record temperature changes over time.
Single channel ECG machine ACT-03M well suited for the purposes of registration the thermo EMF of a thermocouple. Indeed, the electrocardiograph is intended to measure voltages in the range from 0.03 to 4 millivolts (mV). The sensitivity of the device installed the switch and may be 5, 10 and 20 mm/mV. At a speed movement of the tape recorder in 25 mm/s thermal paper roll 50 metre length (Fig. 2) enough for about half an hour of continuous operation, for recreational purposes more than enough.
Fig. 2. The roll of thermal paper 50-meter provides 30 minutes of continuous record the readings
The use of the electrocardiograph as a temperature data logger, in fact, not require any alterations. You only need to have additionally one or several thermocouples and know how to perform all the necessary connections. Despite the fact that the ECG is usually supplied with instructions, dwell on some of the highlights that are important from the point of view of temperature measurement.
First of all, you need to connect to the device network cable and so-called "cable leads", usually consisting of five wires of different colors. According the instructions, when measuring MTS cable wire leads are connected to electrodes: R red - right hand; L yellow - left hand; F green - on the left leg; N black - on the right foot; With white on the chest. For of temperature measurement will use a pair of wires corresponding to the three standard leads: 1. R red L yellow (hand - hand); 2. R red - F green (right arm - left leg); 3. L yellow F green (left hand - left leg).
On the top panel there is a switch that sets the mode measurements for specific room assignment.
Set the switch to the 1st of abstraction and connected to the red and yellow wires findings of the thermocouple. The junction of wires and thermocouples drop in a thermos with ice (below we explain why this is done). Similarly connect the thermocouple to the other two leads - are available to them the corresponding position of the switch. The temperature recorder is almost ready to go.
Where to get the thermocouple? To make it you can own technology, repeatedly described in the technical literature, and to dwell on it in detail it hardly makes sense. But if you have a multimeter, look inside his brand packaging. Many are unaware that the device attached to double thin white wire in the braid with a tiny ball on the end and just is the thermocouple.
Before recording the readings of thermocouples with temperature recorder, should assess the range of possible temperature measurements. Remember - electrocardiograph ACT-03M is designed to measure voltages in the range from 0.03 to 4 millivolts (mV). The thermo-EMF of chromel-kopelevich thermocouples in temperature range from 0 to 100°C varies from 0 to 6.9 mV. Ie thermocouples, in this case, it is logical to measure temperatures of a few tens degrees. Thermo-EMF of chromel-alumel thermocouples in the temperature range from 0 to 100°C varies from 0 to of 4.09 MB. Therefore, it is possible register using the electrocardiograph temperature to 100°C. If use a special platinum-rhodium thermocouples, the upper limit the determined temperature approaching 500°C.
In the measurements using thermocouples need to remember about the amendment at the cold junction (Fig. 3).
Fig. 3. Thermocouple types: 1 - hot end; 2 - cold junction; 3 - the cold junctions (chromel; alumel, copper)
The fact is that during the measurement the temperature of one junction circuit thermocouple, the so-called cold junction must be at 0°C (in a thermos with ice) and the other hot end - in the environment where the temperature is to be measured. Table thermo-EMF of various thermocouples composed specifically for the case when cold junction is at 0°C. If for any reason fails place the cold junction in an environment with a temperature of 0°C and it is at room temperature (for example, at 20°C), in this case, the resulting thermo-EMF corresponds to the temperature difference between the hot and cold junctions and in determining temperature need to introduce the so-called correction cold junction. For this should the measured thermopower be folded with the thermo EMF corresponding to the temperature cold junction (20°C), and the obtained value to determine the temperature using tabular data.
Before switching on the appliance must be installed in the compartment of the tape drive mechanism roll recording paper. The entry signal will be special heat pen is in operation, is heated to approximately 300°C. The electrocardiograph has a dedicated button calibration "1mV" button which will allow you to tape a special calibration signals indicating the sensitivity of the device (Fig. 4). Press "M" tape runs the mechanism of the Registrar and heat the pen writes on the ribbon, change the thermo-EMF thermocouple.
Fig. 4. Record the calibration signal is 10 mm/mV
In Fig. 5 shows the record of testimony chromel-Kobeleva the thermocouple at every second lowering it into a bowl with warm water. Clearly visible growth and the temperature drop of the hot junction at a set of sensitivity and the calibration signal is 10 mm/mV. Chart recorder-temperature data logger based on old cardiograph works.
Fig. 5. A record of temperature fluctuations in 10-15 degrees
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