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Do-it-yourself water pressure gauge. Do-it-yourself homemade electrocontact manometer. Tools and materials

Pressure gauges- devices for measuring the pressure of liquids or gases - come in different designs. A simple measurement of air pressure, for example, in a car or bicycle chamber, can be done by hand. Depending on the power of the spring and the strength of the housing, they can also measure the oil pressure. It is suitable for school experiments in physics lessons. Plus, you can make it with your kids.

You will need

  • - Disposable syringe
  • - Metal spring, the diameter of which is equal to the diameter of the syringe balloon
  • - Needle
  • - Alcohol or gas burner
  • - Glue "Moment"
  • - Pliers
  • - Wire cutters

Instruction

Take a disposable syringe and pull the piston out of it to the limit. Cut the piston rod so that a piece about 1 cm long remains. Heat the remaining piece of the piston rod with gas burner and melt one of the ends of the coil spring into it.

Insert the plunger back into the syringe balloon so that a small piece of the spring remains on the outside, and most of it is inside the balloon.

Warm up the needle and pierce the syringe balloon with it from the side opposite the tip, near the edge. Using pliers, attach the end of the spring to the needle. Bite off the rest of the spring. Got a spring pressure gauge.

If you put a rubber tube instead of a needle on the side of the syringe tip and connect it to the container or pipeline in which the pressure is measured, the piston in the cylinder will move relative to the division scale on the syringe body, thus indicating the pressure in the line or container under test.

It is recommended to first calibrate the scale to a known pressure source. Link the scale to pressure units according to the reference source. To do this, take a tube of transparent material and fill it with water to a certain height. On the other hand, connect the rubber tube to the pressure gauge. Mark the scale according to the height of the water column according to Torricelli's law. In the place where the piston has moved, make a mark of the resulting pressure. After changing the amount of water in the tube, make the following marks.

Diagrams no programs no pressure gauge yes

Having smoked a little these topics: Digital pressure gauge

I realized that many of the motorists are not programmers and not radio amateurs, and not everyone will be able to assemble this digital pressure gauge. I offer a simpler digital pressure gauge that almost every car enthusiast can repeat.

Since all of the above devices are based on voltage measurement. I decided to make friends with a 24 V voltmeter that I have, implemented on a MEGA48PA microcontroller, and a pressure sensor MM370 0-10kg / cm2 with a resistance of 195 ohms. Since we have an upper sensor limit of 10kg / cm2, then I applied a voltage of 10V to the voltmeter and measured the voltage at the input of MEGA48PA 28 leg, it was 0.5 Volt, therefore the measurement limit of 0-10kg / cm2 will correspond to the input of the ADC (28 leg) 0-0, 5V.

Since the resistance of the sensor decreases with increasing pressure from 195 ohms to 0 ohms, it is necessary to redo it a little so that the resistance increases from 0 ohms to 195 ohms with increasing pressure.

Modification of the MM370 sensor for a digital pressure gauge.

Before altering the sensor, the circuit can be drawn as follows, (resistance decreases with increasing pressure)

we need to redo it so that the circuit looks like this (increase in resistance with increasing pressure)

To do this, it is necessary to flare the sensor, I used side cutters.

Before that, it is necessary to put marks on the cover and the sensor body (then it will come in handy during assembly). After disassembly, we see what is inside, namely the measuring element itself and the moving contact. Using a screwdriver, unscrew and remove the measuring element,

it needs to be turned 180 degrees, before that, cutting the contact a little (so that it doesn’t reach the case, I got it)

Test measurements were made, as well as a graph of the dependence of the MM370 resistance on the pressure gauge readings

and plotted (almost linear)

My MM370 (BU) also had a damaged wire,

connecting the movable contact with the body, I replaced it with wiring from a telephone headset.

We assemble and carefully roll (without using a hammer), you can fix it a little by welding (semiautomatic)

REFINEMENT OF THE VOLTMETER

To do this, it is necessary to replace the divider by 28 volts (in my case) in the input circuits of the voltmeter

Since we need a voltage limit from 0 to 0.5V, we use a source reference voltage 5V which is located in the voltmeter itself (the power supply of the MEGA48PA microcontroller is 4 legs) By simple calculations, we need a divider by 10, since the resistance of the MM370 pressure sensor is 195 Ohm, then the resistance for the divider needs 1.95 kOhm, it’s better to put two one of which I set a variable two per 1 room

Now we have three wires on the voltmeter plus + minus - power and pressure measurement.

We connect the pressure gauge to the compressor, calibrate with a variable resistor (for more accurate readings, the calibration must be carried out at the pressure that we expect to use)



How to measure the pressure at the outlet of the reducer:

Those who tried to purchase a pressure gauge to measure low pressure, they know that it is not so easy to do this, and the price for them is not small, 2000-3000 rubles.
How to measure the gas pressure at the outlet of the reducer?
In this article we will tell you about several, fairly budgetary, ways.

Method number 1:
Pressure measurement with a U-shaped manometer

U A -shaped manometer is a liquid manometer consisting of communicating vessels in which the measured pressure is determined from one or more liquid levels.
AT U-shaped glass pressure gauges, the free end of the tube communicates with the atmosphere, and the measured pressure is applied to the other end. The simplest circuit pressure measurement with a liquid glass manometer is shown in the figure:

Atmosphere pressure P atm acts on one end U-shaped tube partially filled with working fluid. The other end of the tube is connected to the area of ​​the measured pressure using various types of supply devices. P abs. At R abs > R atm, the liquid in the part of the measured pressure supplied will be displaced into the part connected to the atmosphere. As a result, between the levels of liquids in different parts U-shaped tube, a liquid column is formed, height h- measured overpressure.

The figure shows U-shaped liquid glass manovacuummeter. U-shaped glass tube 1 is fixed with brackets 2 on a metal or wooden base 3. On it, between the two tubes, there is a scale plate 4 with applied linear markings. The tube is filled with working fluid to the zero mark relative to the scale plate. The bulges at the ends of the glass tube are designed for tighter connection of rubber hoses.

When measuring overpressure to one end U-shaped tube is supplied with the measured pressure medium. The second exit remains free and communicates with the atmosphere. A similar situation occurs when measuring vacuum pressure. The symmetry of the linear markings on the scale plate ensures the applicability of the device for measuring excess and (or) vacuum pressure.
U-shaped liquid manometers with water as a working fluid can be used as pressure gauges, thrust gauges and draft gauges for measuring the pressure of air, non-aggressive gases in the range of ±10 kPa (100 mbar).

You can buy a ready-made manometer with a glass tube. Also, this manometer can be made on your own using a clear PVC tube and ruler.
Naturally, the readings of this pressure gauge will be in mm. water column. To convert them to another value, use the converter at the end of this page.

Method number 2:
Measuring pressure with a household blood pressure monitor

Blood pressure can be measured with a household blood pressure monitor.

1. Take a blood pressure monitor (not a full machine, but one in which the cuff is inflated with a rubber bulb).


2. Disconnect the pear and pick up a piece of hose that will act as an adapter between the reducer and the tonometer hose.


3. Connect the outlet of the reducer to the hose of the tonometer (the valve on the cylinder must be closed)


4. Clamp the hose leading to the cuff (you can use a clamp, a small vise, or, folding the hose several times, pull it with a thread).


5. Press the "Start" button on the tonometer. The tonometer will calibrate and in a few seconds it will be ready for measurement, the display will show “0”


6. Open the valve on the cylinder, the tonometer will show the outlet pressure of the reducer in mm. mercury column. Pay attention to the cuff, it should not inflate.


7. CLOSE VALVE ON CYLINDER.


To convert the resulting value to millibars, use the converter located at the end of the page.

If you have an adjustable reducer and you need to set a certain pressure, follow these steps:
- in the converter of values, enter the required value in millibars
- determine the corresponding value in mm. mercury column
- press the start button on the tonometer, the tonometer will calibrate and in a few seconds it will be ready for measurement, the display will show “0”
- open the valve on the cylinder, the tonometer will show the outlet pressure of the reducer in mm. mercury column
- by adjusting the reducer, set the value you need.
- close the valve on the cylinder

ATTENTION!
Do not use the tonometer for continuous (continuous) measurement of gas pressure.
The materials of which the tonometer is made are not intended for long-term contact with LPG.

Gas Converter:

Soon we will tell you about another simple and inexpensive way to measure low pressure.

Hello! Many people know firsthand about such a measuring device as a pressure gauge. But many find it difficult to imagine the device and the principle of its operation.

The pressure gauge is designed to measure the pressure of a liquid or gas. Moreover, the manometer for measuring the pressure of gas and liquid does not structurally differ from each other. So if you have a pressure gauge lying around somewhere to measure liquid pressure, then you can safely use it to measure gas pressure and vice versa.

To better understand how the pressure gauge works, look at the figure below.

The pressure gauge consists of a body with a measurement scale, a copper flat tube 1 rolled up in the shape of a circle, a fitting 2, a transmission mechanism 3 from the tube to the arrow 4. Using the fitting, the pressure gauge is wrapped in a vessel where the pressure of the medium (gas or liquid) is to be measured.

How a manometer works

When gas and liquid under pressure are supplied through fitting 2, the rolled tube 1 will tend to straighten out, while through the transmission mechanism the movement of the tube will be transmitted to the arrow 4. It, in turn, will indicate the pressure value, which can be read using the scale. When the pressure decreases, the tube will again curl up and the arrow will indicate a decrease in pressure.

Electrocontact pressure gauge device

How the electrocontact pressure gauge works, I think you guessed it yourself. It does not differ in any way from a conventional pressure gauge, only with the exception that it has built-in contacts. There are usually two of them and their position on the pressure gauge scale can be changed.

And if you do not have an electrocontact pressure gauge, but you really need it? What to do then? Then you need to make a homemade electrocontact pressure gauge.

I will tell you how to make a homemade electrocontact pressure gauge. To do this, you will need a simple pressure gauge, two small strips of tin from tin can, double-sided tape and two thin wires.

Use a sharp awl to pry and remove the large retaining ring. Then remove the glass and then the rubber washer. Drill two holes in the gauge body to allow two wires to pass through.

Cut two strips from the tin and bend them in the shape of the letter L. Solder a thin insulated wire to the base. From double-sided tape, cut two strips equal in size to the strips and stick it on the strips. Next, glue the resulting contacts to the pressure gauge scale within the specified pressure limits.


Pass the wires through the holes and bring them out.

Replace the rubber gasket and then the glass. Secure everything with a retaining ring. Everything, a home-made electrocontact pressure gauge is ready. For example, I used this one in a homemade automatic system water supply of a private house.

Wiring diagram for electrocontact pressure gauge

In order for this manometer to act on any actuating mechanism, you need a special scheme. You can see an example of this circuit in the figure below.

At the minimum pressure of the medium (gas or liquid) in the electrocontact pressure gauge, contacts 1 and 2 will be closed. In this case, the electromagnetic relay K1 will work. It, in turn, with its contacts K1.1 will supply power to the winding of the magnetic starter K3. With contacts K3.1, it will shunt contacts K1.1, while opening the contacts in the pressure gauge 1 and 2, relay K1 releases its contacts K1.1. But at the same time, the winding K3 of the starter will continue to flow around with current. With its contacts K3.2, the magnetic starter will supply power to the motor M of the pump or compressor.

With a further increase in pressure in the pressure gauge, contacts 1 and 3 close. In this case, the electromagnetic relay K2 will operate and open the power supply circuit of the coil K3 of the magnetic starter with its contacts. Contacts K3.2 will then open and the power supply to the motor M will disappear. With a further decrease in pressure and the closure of the pressure gauge contacts 1 and 2, the cycle will repeat.

... I decided to write a strange post. Somehow, a post about the manufacture of a pressure gauge caught my eye. Or rather, not the device itself, but its miniature copy. For what? For all sorts of crafts where you don’t need to use these devices (and it’s unlikely that you can find them in this size).

MANOMETER (from the Greek manos - loose and metron - measure, metreo - I measure), a device for measuring the pressure of liquids and gases. Depending on the design of the sensitivity of the element, there are liquid, piston, deformation and spring pressure gauges (tubular, membrane, bellows);

dependences of some physical quantities (eg, electric current strength) on pressure are also used. There are absolute pressure gauges - they measure absolute pressure (from zero), gauge pressure gauges - measure the difference between the pressure in any system and atmospheric pressure, barometers, differential pressure gauges, vacuum gauges.


A “cork” is cut out of the gum using a tube. Later, we will need it as a substrate for the pressure gauge scale.

We cut the tubes of the diameter we need. One tube is slightly larger - this will be our body. The second tube is smaller. It will serve as a stopper for the rear wall on one side and the glass on the other.


We make an elastic band of such thickness on which we want to place the scale of the device.

We cut out the image of the desired scale, suitable in size. I made scales in advance. I collected pictures from the network, removed everything unnecessary, made several images of the same scale of different sizes and printed them in the nearest photo kiosk.


For glass we take any transparent plastic. I used a CD box. We cut a circle along the inner diameter of a wide tube with side cutters. We adjust with a file. The glass should go in very tightly, then glue will not be needed.

We make from a brass plate back wall. It should be the same diameter as the glass.

Let's start assembling the product. First, glue the back wall to the end of the smaller tube. Then we glue the tubes so that one is in the other, while the bottom should be flush with the end of the larger tube. We drill a hole in the body.

AT drilled hole we insert the wire, on both sides of which we place the halves of our substrate, Glue.

From thinner wire we make a decorative ring that will hide the edges of the paper scale.

We shorten the second hand from the wrist watch to suitable sizes and put it on the scale.

This is what the reverse side of our device looks like. On the wire coming out of it, you can put on a thin tube shorter. The part of the wire not covered by the tube will later be inserted into the tank (or into that part of your craft, on which the installation of this dummy is planned).

It remains to grind the body and insert the glass.

You can simplify the task by using these nuts as a body.

Result.