Device and principle of operation of pressure sensors, expense and level
The majority of sensors the davleyoniya are under construction on the principle of transformation of pressure to mechanical movement. Except mechanical systems which memyobrana and tubular springs enter also electric and thermal systems are applied to measurement of pressure.
With the mechanical perceiving bodies treat pressure sensors:
- liquid pressure sensors (U-shaped systems);
- piston systems;
- spring systems: a) membrane (flat, corrugated, soft); b) sylphons; c) manometrical tubular springs.
Let's consider the device of some most often found pressure sensors.
Spring pressure sensors are most widely used. Their action is based on the vozniknoveyoniya of elastic deformation of the pruyozhina which is the chuvstviyotelny element of the device. Deformation arises at pressure izmeneyoniya in or outside of the spring. Change of the form of the element is transferred to the mobile part of the device with the arrow moving on the scale, at removal of pressure the sensing device takes the initial form.
In technical manometers and vacuum meters elastic springs are usually applied: single-turn, multi-turn, flat membranes and sylphons (garmonikovy membranes).
In fig. 1 types of spring pressure sensors are shown.
The single-turn tubular spring (a) is bent on the arch almost in the form of the circle approximately on 270 °. In section the spring has the ellipse appearance. It from brass is produced (or steel - for big pressure). One end of the spring is soldered and is free. The second end of the spring is not mobile, and the measured pressure of river is brought to it. Pressure causes deformation of the spring and the peremeyoshcheniye of its free end.
Untwisting of the spring happens for the following reason. At increase in internal pressure elliptic section streyomitsya to take the round form, i.e. the small axis of the ellipse begins to increase, and big - to decrease. Tension which will untwist the tubular spring result. The free end of the spring will proporyotsionalno move at the same time to pressure in it. Thus, the measured davyoleniye will be transformed to mechanical movement of the free end of the spring. The size of this movement usually is 5 — 7 mm.
The multi-turn tubular spring (b) has 6-9 rounds with a diameter about 30 mm. Movement of the free end of the spring much more (up to 15 mm), than at the single-turn spring. Also the towing capacity is much bigger here.
Usually sensors in the form of the single-turn tubular spring are used in pokazyvayuyoshchy devices, and sensors in the form of multi-turn tubular springs - in self-recording. This results from the fact that in self-recording priyobor the sensor has to possess the big effort sufficient for overcoming friction not only in joints of the transfer and multiplying mechanism, but also friction of the feather about paper.
The flat corrugated membrane (v) is used or otyodelno, or in the box from two corrugated membranes. Also soft membrane from the flat rubberized fabric connected to the flat calibrated spring Primeyonyatsya.
The Garmonikovy membrane — the sylphon (g) represents the cylindrical box with the walls having uniform cross folds (corrugations). The measured pressure moves in the sylphon or outside of it.
In comparison with the flat membrane and the membrane box the garmonikoobrazny membrane possesses the greatest chuvstvitelyyonost.
Sylphon devices intend for measurement and record of excessive pressure and depression. Besides, these devices isyopolzutsya as secondary devices to devices, the snabyozhenny device for pneumatic transfer of indications on distance.
Spring pressure sensors in schemes of automation preobrayozut mechanical moving to the electric signal at poyomoshch of inductive, rheostatic or contact sensors.
The scheme of the MED pressure sensor is provided on fig. 2. Pressure perceived tubular manometrical pruzhiyony 1 will be transformed to movement of the end of the manometrical trubyoka. This movement is transferred to the plunger of the transformer sensor 2. The secondary device is the EPID device.
Flow rate sensors happen mechanical, thermal, ionization, induction, acoustic.
Mechanical flow rate sensors are separated into sensors of pereyomenny and continuous difference and also sensors with drain otyoverstiy.
Flow rate sensors of variable difference operate by the principle of emergence of differential pressure in the narrowing device which is installed on the way of the moving environment. Pereyopad of pressure is function of the expense here. The narrowing device is the perceiving body of the flow rate sensor.
Flow rate sensors of continuous difference (rotameters) use the narrowing bodies for regulation of section for the purpose of support to constants of the pereyopad of pressure.
The scheme of the rotameter with the inductive sensor is provided on fig. 3. The rotameter consists of the koyonichesky tube 1 and the float 2. At fluid movement or gas in the ring gap between the float and walls of the tube differential pressure which creates force operating towards to float weight force is created. The provision of the float in the conic tube is defined by expense size.
Rotameters are carried out as detection instruments and as datyochik. The winding of the inductive sensor is placed outside on the nozzle tube. The iron float is the core of the coil 3 of the inductive sensor. At change of the expense the float peremeyoshchatsya and changes inductance of the coil, thus the expense will be transformed to the electric signal.
Float-operated sensors are extremely widespread. The float-operated sensor consists of the float - the body perceiving the fluid level; promeyozhutochny body - the mechanical communication transforming and overeating mechanical influence to output body, predstavyolyayushchy itself the movement sensor.
Sensors of level can be based on measurement of weight and hydrostatic pressure of liquid, on use of electrical properties of liquid (change of resistance, the emyokost, inductance).
The domestic industry releases sensors of level of razyolichny types.
In fig. 4 the scheme of the float-operated datyochik of level with the rheostatic sensor R is given in the exit. According to indications millivoltmetramv judge the fluid level of N in the vessel.Top