And the fact that you get used to everything and that with whom you will lead from that and you will gain are common truths. So I got used to my multimeter, and when someone grabs it (excuse me, it takes to use it) - “the toad strangles me”. I can’t say anything, it was from me that the household picked up a certain amount of the amateur radio virus and now have a need to measure the voltage of the batteries in the remote control, the battery in the phone, etc. I endured. Until I heard that some citizens are interested in the voltage at the sockets.
I don't remember where this measuring head came from, but I always thought it was "killed to zero" - I was wrong. When checking it, it turned out that it was completely adequate. That's just the look ...
Disassembled to the maximum. I washed the body, glued the upper part. With the tip of the blade of a small clerical knife, I scraped off the extra zeros from the scale. The result is a 15 volt scale. Instead of 150k resistance, I soldered a jumper into the block. The broken tip of the arrow was put back in place with a piece of insulation and glue.
The arrow, of course, needed balancing. I made, according to the following technology of balancing the arrow, the existing counterweights with droplets of solder on them (we move with a well-heated soldering iron, these same droplets).
- Where to move- we place the arrow horizontally and see what outweighs, if the arrow, then move the drop from the center. If the counterweight is a drop towards the center.
- Which drop to move- place the arrow vertically.
- a) you need to move "to the center". The arrow has deviated to the right - move the right drop. Left - left.
- b) you need to move "from the center". The arrow has deviated to the right - move the left blob. Left - right.
I filled the existing grooves in the upper part of the case with plastic with a soldering iron and leveled it with a file, then with a fine and then the smallest sandpaper, finally painted and pasted the cut glass into it with glue. I also painted the inner metal strip (so that everything was in color), dried and assembled.
External charm has appeared. And to give a technical sophistication, I supplemented the measuring head with a three-position switch and three resistors.
The measuring head has become the owner of three measurement limits: at 3, 15 and 30 volts. Here is a picture of the printed circuit board and part-time circuit:
I will dwell on the moment of assembly. As it turned out, learning how to knock out the compound from the gap between the lower and upper parts of the measuring heads and thus separate them is not a problem, the problem is to connect them. Well, do not bother, in fact, filling them with a new compound. I connect like this:
In the very corner, I drill a hole slightly smaller in diameter than the prepared self-tapping screws (exclusively aluminum) and ... And if anyone is embarrassed by the possibility of dust penetrating inside, then there is plasticine for this. When the meter was ready (called it the first level voltmeter), he instructed those involved and gave it out for use. I liked the device, especially because there is only one "button". I asked you not to push the probes into the outlet - it's better to immediately have carnations. Wishing you success, Babay.
Discuss the article POINT VOLTMETER
BMK-Micha, the main drawback of this device is its low resolution - 0.1 Ohm, which cannot be increased purely by software. If not for this drawback, the device would be perfect!Ranges of the original circuit: ESR = 0-100Ω, C = 0pF-5000µF.
I would like to draw your attention to the fact that the device is still in the process of finalizing both software and hardware, but it continues to be actively used.
My modifications regarding:
Hardware
0. Removed R4, R5. Reduced the resistance of resistors R2, R3 to 1.13K, and matched a pair with an accuracy of one ohm (0.1%). Thus, I increased the test current from 1mA to 2mA, while the nonlinearity of the current source decreased (due to the removal of R4, R5), the voltage drop across the capacitor increased, which contributes to an increase in the ESR measurement accuracy.
And of course Kusil corrected it. U5b.
1. Introduced power filters at the input and output of the converter + 5V / -5V (in the photo of the scarf it is standing vertically and there is a converter with filters)
2. put the ICSP connector
3. introduced the R / C mode switch button (in the "original" the modes were switched by an analog signal coming to RA2, the origin of which is described in the article extremely vague ...)
4. Introduced forced calibration button
5. Introduced a buzzer confirming pressing of the buttons and giving an on signal every 2 minutes.
6. I have empowered the inverters with their parallel pairwise connection (with a test current of 1-2mA it is not necessary, I just dreamed of increasing the measurement current to 10mA, which has not been possible so far)
7. In series with P2 I put a resistor of 51 ohms (in order to avoid short-circuit).
8.Exit. I shunted the contrast adjustment with a 100nf capacitor (soldered to the indicator). Without it, when the P7 engine was touched with a screwdriver, the indicator began to consume 300mA! The LM2930 almost burned along with the indicator!
9. I put a blocking capacitor on the power supply of each MC.
10. Adjusted the PCB.
Software
1.removed DC mode (most likely I will return it back)
2. Introduced a tabular nonlinearity correction (at R> 10 Ohm).
3. limited the ESR range to 50 Ohm (with the original firmware, the device went off scale at 75.6 Ohm)
4. added a calibration routine
5.wrote support for buttons and buzzer
6. introduced the indication of the battery charge - numbers from 0 to 5 in the last digit of the display.
Neither software nor hardware interfered with the capacitance measurement unit, with the exception of adding a resistor in series with P2.
I have not yet drawn a schematic diagram reflecting all the improvements.
the device was very sensitive to moisture! as you breathe on it so the readings begin to "float". This is due to the high resistance R19, R18, R25, R22. By the way, can someone explain to me why the cascade on U5a has such a large input impedance ???
In short, I filled the analog part with varnish - after which the sensitivity completely disappeared.
ELEKTOR magazine as far as I know is German, the authors of the articles are Germans and they publish it in Germany, at least the German version.
m.ix let's joke in the flame
A simple kilovoltmeter for measuring voltages up to 50 - 100 kilovolts and more can be made by yourself. Such a device can be useful when adjusting the modes of cathode-ray tubes, air ionizers, flokators and other devices where high supply voltages are used.
For the manufacture of a kilovoltmeter, the following main components are required:
A hollow fiberglass ski stick (Such sticks were once sold complete with the most budget skis. It is possible that such a stick is lying on your balcony).
High-voltage resistors type C3-14-1- (B) (It is these resistors that exactly fit the inner diameter of the ski pole).
Multimeter "Chinese" with an input resistance of 10 megohms. Multimeters smaller than the one shown in the picture tend to cost less and have an input impedance of only 1 megohm.
Some small details.
Diagram of a kilovoltmeter.
Resistors R1 - Rn - upper arm of the voltage divider;
- Resistors R * (rough), R * (accurate) and the input resistance of the measuring device (10 MΩ) - the lower arm of the divider.
- A neon lamp protects the kilovoltmeter from exceeding the safe voltage in the lower arm of the divider when the latter is cut off. If the calculated voltage supplied to the multimeter is higher than 50 Volts (for example, 100 Volts), then one more neon lamp should be connected in series.
About the resistors of the upper arm of the divider.
Resistors C3-14-1 (group B) These are one-watt resistors that can withstand voltages up to 10 kilovolts. Resistance range from 470 MΩ to 5.6 GΩ. When buying, you should be aware that these resistors are not very reliable, both in operation and during storage. Therefore, it is better to purchase them with some margin. I would recommend buying twice the amount required.
How to calculate a high voltage divider?
In amateur practice, most often, it is necessary to assemble such devices based on the available parts. Therefore, it is necessary to proceed to the manufacture of a high-voltage divider probe only when the resistors are purchased and tested. Based on the available high-voltage resistors, the final calculation of the divider should be made.
An approximate, preliminary calculation of the upper arm of the divider.
We choose the limiting voltage, for example, 50 kilovolts. With this voltage, we need to use 5 - 6 resistors, each of which can withstand up to 10 kilovolts.
We calculate the voltage divider for the multimeter scale, for example, 200 volts. For ease of reading, it is desirable that 1 kilovolt of the measured voltage falls on 1 volt of the scale.
The input resistance of the multimeter is 10 megohms. However, to set up the divider, we need to bypass this shoulder.
Therefore, let us take this shoulder equal, for example, 8 MOhm.
8 (MΩ) * 50,000 (Volt) / 50 (Volt) = X + 8 (MΩ)
X = 7992 MOhm
7992 (MOhm) / 6 (pieces) = 1332 MOhm
Of course, you will hardly be able to find the required resistor rating and you may have to choose from commercially available resistors. The divider can also be assembled from different resistor values, but then you need to calculate the voltage drop for each resistor. From my experience, I can add that the C3-14-1-B resistors, with their length of 29mm, can withstand a voltage of one and a half or even twice the permissible, but their reliability decreases.
In order to reduce the current flowing through the kilovoltmeter, you can increase the resistance of the upper arm of the divider by an order of magnitude or two. In this case, you will need to select the scale of the device, respectively, 20 Volts or 2 Volts.
Preliminary calculation of the shunt to the multimeter (R * rough + R * exactly).
R tester + R shunt = 8 megohms;
R shunt = 10 * 8/10 - 8 = 40 (MOhm)
Sectional drawing of a part of a kilovoltmeter probe.
Sectional drawing of a part of a kilovoltmeter probe.
1. Tip;
2. Nut;
3. Getinax or fiberglass washer (suitable from the attachment point for the PEV resistors);
4. Metal bushing with thread inside (any suitable size with internal thread M2.5 - M3 (mm) will do;
5. A female connector of a suitable size for connection to the high voltage resistor terminal. The connector is required so that during the operation of the device it is easy to replace a failed resistor;
6. The first resistor of the upper arm of the divider;
7. A piece of a ski pole (I recommend choosing the length of the workpiece depending on the previously calculated and already available number of resistors).
We proceed to the final assembly.
First, we make the tip fastening assembly, for which we solder the connector "5" to the sleeve "4".
Then we glue the parts "3" and "4" into the end of the tube using epoxy resin.
When gluing, make sure that the epoxy does not flow into the "5" connector.
We solder the resistors of the upper arm of the divider in series and insert it inside the ski pole so that the first resistor goes into the connector located inside. We fix the last resistor by soldering at the base of the probe.
We collect the rest of the circuit elements by placing them in a suitable metal or plastic box.
1. Two terminals for ground connection;
2. Connector CP-50 for connecting a tester or an oscilloscope;
3. Resistor R * (rough);
4. Resistor R * (exactly);
5. Neon lamp;
6. Replaceable tip.
We calibrate the divider.
For calibration, it is convenient to use a 1000 volt constant reference voltage source, since this is the maximum voltage that can be measured, usually with the instruments available to the radio amateur. If this is not available, then you can use another less high-voltage source.
Calibration is reduced to the selection of resistors in the lower and upper arms of the divider. The spread in the parameters of high-ohm resistors is large, so it may be necessary to re-calculate the results of the preliminary calibration in order to make corrections.
Using a kilovoltmeter.
1. Kilovoltmeter probe assembled;
2. Wires for connecting ground and multimeter;
3. Two types of tips;
4. An example of connecting a kilovoltmeter to the anode of a kinescope using a replaceable tip in the form of a hook.
When using the device, follow the safety precautions.
Connecting and disconnecting the kilovoltmeter should be done with de-energized equipment, after removing the charge from high-voltage current-carrying parts.
When connecting the kilovoltmeter to the measured circuits, connect the ground first!
When disconnecting the probe from the circuits being measured, disconnect the ground connection last!
When connecting the kilovoltmeter to the anode of the kinescope, one ground terminal should be connected to the graphite coating of the kinescope, and the other to the common wire of the TV chassis.
info - oldoctober.com/ru/kilovolt