THE SECOND PROFESSION OF AN ELECTROCARDIOGRAPH

In the process of creating Amateur designs may require tools and equipment that are available it is often difficult. In such cases, comes to the aid of ingenuity, and craftsmen are doing everything they can with their hands. We will talk about how you can make a real recorder-thermoregulator from the old electrocardiograph type ЭК1Т-03M (Fig. 1).

This device may be required to measure and record the temperature of specific areas (details) for some time. Explain with an example. Collecting a powerful computer with your hands, you may face the problem of overheating of the processor. For cooling it will need a cooling system, which obviously eliminates the risk of failure of the “computer brain”. Well, if you own appropriate methods of calculation. And if not? You can, of course, immediately turn on the computer and “burn” the CPU or not? PI is unlikely you will meet the sad outcome of such an experiment… it is Much better to check the efficiency of the cooling system under model conditions by measuring the temperature rise of the radiator, which subsequently will be contacting the processor. Using the model heat source and thermoregulator, you will easily be able to choose the design parameters under which the processor will be guaranteed from overheating.

 

It is useful to mention the principle of operation of a handmade thermoregulator. In the technique well-known methods of measuring temperature using thermoelectric thermometers (thermocouples). A thermocouple consists of two conductor of different material, the components of the shared electrical circuit (see Fig. 3). If the temperature of joints (junctions) of the thermocouple are not the same, then there is thermo-EMF and the circuit current flows. Thermal EMF is greater, the greater the temperature difference between the junctions. By connecting the thermocouple with recorder, get a device that allows you to record changes in temperature over time.

 

Single channel electrocardiograph ЭК1Т-03M well suited for the purposes of registration of thermal EMF of the thermocouple. Indeed, the ECG unit designed to measure voltages in the range from 0.03 to 4 millivolts (mV). The sensitivity of the device set by the switch and can be 5, 10 and 20 mm/mV. If the speed of the tape recorder at 25 mm/roll thermal paper 50-meter length (Fig. 2) lasts about half an hour of continuous operation which for recreational purposes is more than enough.

 

The use of the electrocardiograph as a temperature logger, in fact, requires no alterations. You only need to have additionally one or more thermocouples and know how to perform all the necessary connections. Despite the fact that the electrocardiograph is typically applied with manual, focus 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 the network cable and the so-called “cable leads,” usually consisting of five wires of different colors. According to the manual, when measuring kardiogramm cable wire leads connected to the electrodes: R red – right hand; L yellow left arm F green left leg; N black – on right leg; With white on the chest. To measure temperature we use a pair of wires, corresponding to the three standard leads: 1. R red L yellow (hand – arm); 2. R red F green (right arm – left leg); 3. L yellow – F green (left hand – left foot).

 

On the top panel there is a switch that sets the mode to a specific number of leads.

 

Set the switch to position 1, the drain and connected to the red and yellow wires on the findings of the thermocouple. The connection of the wires and thermocouples was lowered into the flask with ice (below we explain why this is done). Similarly, connect the thermocouple to the other two leads – they have the appropriate switch position. Thermoregulator almost ready to go.

 

Where can I get a thermocouple? To make it you can own technology, repeatedly described in the technical literature, and to elaborate on that here hardly makes sense. But if you have a multimeter, then look inside its packaging. Many are unaware that the device attached to a double thin wire in a white sheath with a tiny ball on the end is just the thermocouple.

 

Before recording the readings of the thermocouples with the help of thermoregulator, should evaluate the range of possible temperature measurements. Remember – ECG ЭК1Т-03M is designed to measure voltages in the range from 0.03 to 4 millivolts (mV). At the same thermo-EMF chromel-kopelevich thermocouples in the temperature range from 0 to 100°C changes from 0 to 6.9 mV. That is such a thermocouple, in this case, it is logical to measure the temperature several tens of degrees. Thermo-EMF chromel-aljuminievyh thermocouples in the temperature range from 0 to 100°C changes from 0 to 4.09 MB. Therefore, it is possible to register using electrocardiography temperature to 100°C. If use the special platinum-rhodium thermocouples, the upper limit is determined by the temperature closer to 500°C.

 

When measuring with thermocouples it is necessary to remember about the amendment to the cold junction (Fig. 3). The fact that in the process of measuring the temperature of one junction of the thermocouple circuit, 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 of thermo-EMF of various thermocouples is made for the case where the cold junction is at 0°C. If, for any reason, fails to place the cold junction in an environment with a temperature of 0°C and it is at room temperature (e.g. 20°C), in this case, the occurring thermo-EMF to the temperature difference between the hot and cold junctions and for determining the temperature it is necessary to introduce a correction for the cold junction. To do this, the measured thermo-EMF to lay down thermo-EMF corresponding to the cold junction temperature (20°C), and according to the obtained value to determine the temperature using tabular data.

 

Before switching on the appliance must be installed in the compartment tape transport registered a roll of thermal paper. The record will be made of a special heat pen, which in the process is heated to about 300°C. the ECG unit has a dedicated calibration button “1mV”, which when pressed will allow you to tape a special calibration signals, indicating the sensitivity of the instrument (Fig. 4). Click the “M” starts the tape drive mechanism of the Registrar and heat the pen writes on the tape a change of the thermal EMF of the thermocouple.

 

Fig. 4. Record calibration signal of 10 mm/mV

 

Fig. 5. The record of fluctuations of temperature 10 – 15 degrees

 

In Fig. 5 shows the record of the testimony chromel-Kobeleva the thermocouple every second when lowering it in a bowl with warm water. Well seen the rise and fall of the hot junction temperature if you set the sensitivity and calibration signal of 10 mm/mV. The recorder-temperature recorder on the basis of the old cardiograph works.

 

LITERATURE

 

1. Electrocardiograph ЭК1Т-03M. Technical description and manual, 2nd edition, 1985

 

2. Theory and technique of thermo-physical experiment, Moscow, Energoatomizdat, 1985.

 

3. Zubarev V., Alexandrov A., Okhotin V. Workshop on technical thermodynamics, Moscow, Energoatomizdat, 1986