Monthly Archives: August 2016

Pressure Measurement Devices

Pressure Measurement Devices

Different types of Pressure Measurement Devices

Gravitational transducers

  1. A dead weight tester
  2. Manometer

Elastic TransducersPressure Measurement Devices

  1. Bourdon tube pressure gauge
  2. elastic diaphragm gauges
  3. bellow gagues
  4. Bellow gaugues to measure gauge pressure
  5. Bellow gauge to measure differential pressure

Strain gauge pressure cells.

    1. Flattened tube pressure cell (PINCHED TUBE).
    2. Cylindrical type pressure cell.

Mcleod vacuum gague.

  1. Thermal conductivity gauges.

Pirani gauge.

  1. Thermocouple typre conductity gauge.

Ionisation gauge

  1. bulk modulus or electrical resistance pressure gauge.

 

The above Pressure Measurement Devices are used in following situations:

 

Type of pressure to be measured Pressure Measurement Devices to be used
Low pressure Manometer
High and medium pressure Bourdon tube pressure gauge.

Diaphragm gauge.

Bellows Gauges.

Low vacuum and ultra high vacuum Mcleod vacuum gauge

thermal conductivity gauges.

Ionisation gauges.

Very high presures Bourdon tube pressure gauge.

Diphragm gauge.

Bulk modulus pressure gauge.

Terms related to pressure

Terms Related To Pressure

Terms Related to Pressure

Atmospheric pressure:

The pressure due to air surrounding the earths surface is called as atmosperic pressure.

Absoulte pressure:

It is known that pressure is force per unit area when the interaction of fluid particles among themselves is zero, a zero pressure intensity will occur. This is possible only when the population of molecules is negligibly small which is nothing but perfect vacuum. Hence the pressure intensity measured from a state of prefect vacuum is called as absoulte pressure.

Terms Related To Pressure

Gauge Pressure:

A pressure measuring instrument generally measures the difference between the uknown pressure (p) and the atmospheric pressure (pa). When the unknown pressure (P) is greater than the atmospheric pressure (Pa), the pressure measured by the instrument is called as the gauge pressure.

Vacuum pressure:

A Pressure measuring instrument generally measures the difference between the unknown pressure (P) and the atmospheric pressure (Pa). When the atmospheric pressure (Pa) is greater than the unknown pressure(P), the pressure mesured by the instrument is called as the vacuum pressure.

Static Pressure:

The pressure caused on the walls of the pipe due to a fluid at rest inside the pipe or due to the flow of a fluid parallel to the walls of the pipe is called as static pressure. This static pressure is measured by inserting a pressure measuring tube into the pipe carrying the fluid, so that the tube is at right angle to the fluid flow path.

Terms Related To Pressure

 

Total or Stagnation pressure:

These are one of the Terms Related To pressure Pressure which is obtained by bringing the flowing fluid to rest isentropically is called as total or stagnation pressure. Hence the pressure will be a sum of static pressure and impact pressure.

Dynamic – or – Impact – or – Velocity pressure.

The pressure due to fluid velocity (flow speed) is called as impact pressure.

Impact pressure = Total pressure – static pressure.

These are some of the Terms Related To Pressure

Pressure Measurement Introduction

 Pressure Measurement Introduction

 Pressure Measurement

In general, pressure is represented as force per unit area. The measurement of pressure is one of the most important measurements, as it is used in almost all industries. Some important appilications of Pressure Measurement is listed.

1. The pressure of steam in a bolier is measured for ensuring safe operating condition of the boiler.
2. It is done in continous processing industries such as manufacturing and chemical industries.
3. Pressure Measurement helps in determining the liquid level in tanks and containers and density of liquids.
4. In many flow meter (such as venturimeter, orifice meter, flow nozzle, etc.,) pressure measurement serves as an indication of flow rate.
5. Measurement of pressure change becomes an indication of temperature (as used in pressure thermometers-fluid expansion type).
6. Apart from this, Pressure Measurement is also required in day-to-day situations such as maintaining optimal pressure in tubes of vehicle tyres.

Definition of pressure:

Pressure is the force exerted by a medium (fliud) on a unit area due to the interaction of fluid particles amongst themselves.

The following are the terms related to pressure namely:
1. atomspheric pressure.
2. Absolute pressure.
3. Gauge pressure.Pressure Measurement
4. Vacuum pressure (Rare fraction or negative pressure).
5. Static pressure.
6. Total or stagnation pressure.
7. Dynamic or impact or velocity pressure.

The next post will describe in detail about the above terms.

Pressure Gauge Calibration

Pressure Gauge Calibration

Pressure Gauge Calibration Pressure Gauge Calibration: Things to Know!

Before getting into the intricacies of pressure gauge calibration it’s really important to know what calibration means. Do you know what calibration is? Well, calibration is a process of determining equipment’s measuring accuracy. The process involves obtaining a reading from the instrument and measuring its variation from the reading obtained from a standard instrument. Calibration of several instruments also deals with adjusting the precision and accuracy to make sure that the readings come in parity with the established standard. Similarly, pressure gauge calibration signifies a process to determine the measuring accuracy of a pressure gauge.

Pressure Gauge Calibration Procedure

It’s essential to have an understanding of the pressure gauge calibration procedure to get a proper idea about the pressure gauge calibrator. A typical pressure gauge measures the performance of the gauge at between 5 and 10 pressure points which is spread across equally on the scale for both rising and falling applied pressures. Usually, these pressures fall on the main scale markings for an analogue gauge or at a suitable interval for a digital gauge. The gauge should be taken around the pressure cycle from zero to full scale and back at least once before going ahead with the calibration measurement. This helps to find out whether the gauge has a major fault that would prevent calibration.

The gauge reading at each calibration point is calculated for both rising and falling pressure. Rising pressure means the lowest pressure point on the gauge which is increasing steadily until the calibration pressure point is reached. Falling pressure means starting at the maximum pressure point on the gauge and then gradually decreasing the pressure to the calibration pressure point. When the desired point is reached on the scale, the pressure is held steady and the gauge reading is considered. The operator mustn’t hurry and should wait until both the applied pressure and gauge reading have stabilised before recording a reading.  This method is followed for all different types of gauge.

Pressure Gauge Calibration Equipment

There are more than one pressure gauge calibration equipment. To know more, keep reading below:

  • Deadweight Testers- They offer the most accurate measurement of pressure. No other equipment can match the stability, continuity and accuracy of the deadweight tester. It is apt for calibrating pressure transducers, pressure gauges, recorders, and so on. It can be sub-divided into the following below-mentioned testers-

a)      Oil operated deadweight testers

b)      Gas driven oil lubricated deadweight testers

c)       Differential gas driven oil lubricated deadweight testers

 

  • Gas pressure Regulators- These are used to control and regulate the gas pressures. They play a major role in a combination with gas deadweight testers and also can be used for other calibration purposes. 
  • Comparison Test Pumps- These are portable and rugged pumps for checking pressure instruments against a master test gauge or transducers.
  • Accessories- Like dirt/moisture trap, oxygen tester, instrument stand, adapters.

Pressure Gauge Calibration Frequency

The calibration frequency of the pressure gauge should be kept within shorter intervals to reduce the risk of wrong measurements. There are several factors that determine the frequency of calibration in measuring the accuracy and these are as follows-

  • Usage of the pressure gauge
  • The environmental conditions where the pressure gauges are stored and used.

Uncertainties in measurement.

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Carbon Dioxide Gas Detectors – CO2 detectors

Know about the Carbon Dioxide Gas Detection System

Carbon Dioxide Gas Detectors – CO2 detectors

The infrared spectroscopy is actually based on the concept of gas molecules that absorb infrared light and other gases that occur at a specific wavelength. Usually, a thermopile which has a built-in filter is useful to detect the specific amount of gas. For example, carbon dioxide is considered to be a strong gas which has a high absorption rate at a wavelength of 4.26 µm. A band filter is put to use so that it can remove the existing light out from the wavelength. Gas molecules also have the ability to absorb radiation energy emitted from the lamps. The absorption rate follows the Lamber-Beer law which is I = Io*e –kcl.

A little elaboration of this law always helps readers to get better clarity. I is the transmitted infrared (IR) from the thermopile detector side. The Io is initial intensity at the IR source. k is the gas absorption coefficient. c is the gas concentration. I is the length of the absorption path from the light source to the thermopile detector.

The thermopile is effective in finding the light intensity change. The output voltage will be –

V = n * Δα * (Tbody – Tamb)

Over here Δα is the difference in the Seebeck coefficients in the thermopile materials. n is the number thermocouples in the thermopile detector. Tbody is the blackbody temperature which emits thermal radiation and Tamb is the temperature of the surrounding ambient.

Within the chamber, the infrared (IR) lamp radiation is considered as the ideal black body radiation. The radiation a blackbody emits is a result of the difference in temperature between the ambient and the blackbody, this entire process is known as thermal radiation. As per the Stefan-Boltzmann law, the thermal radiation per unit area is –

RT = σ * (Tbody4 – Tamb4)

Over here σ = 5.67 * 10-8 W/(m2 *K4) is the Stefan-Boltzmann constant. For better understanding, let us assume that there is no loss in light intensity while it travels through the chamber, in such a situation RT = I. So, let us rearrange the entire equation and the thermopile output voltage becomes:

V = n * Δα * [I0 * e -kcl ] / [σ * (Tbody2 + Tamb2 ) * (Tbody + Tamb)]

Examining this equation will help us understand that thermopile output voltage will get affected because of the ambient temperature along with the complex relationship because of the uncertainty in the lamp intensity. In order to get better accuracy, special attention needs to be given to the design implementation. The temperature compensation is the best way to maintain accuracy in the system. In order to accomplish this, the thermistors are integrated into the thermopile sensor and there are changes in the resistance which depends on the ambient temperature of the surrounding. To get accuracy in measurement it is important to have a constant and steady voltage that can successfully excite the thermistor.

The carbon dioxide gas detection system is an important feature and it is important to have an in-depth understanding of the same.

Traditional Discrete Op Amp Signal Conditioning

The traditionally discrete amps are used for the NDIR systems and the AC coupling helps in removing the signal chain offset. In order to successfully handle a two-channel, it is essential to use a quad op amp that can be configured in a dual change on the front end. Active filtering also needs to be built in the signal path.

Carbon Dioxide Gas Detectors

NDIR is an industry term known as non-dispersive infrared and is considered to be the most common type of sensor that is used to effectively measure carbon dioxide. Infrared lamp directs the waves of light into a tube filled with air towards the IR light detector. This light detector measures the right amount of infrared light that hits it successfully. When the light passes through the tube, the gas molecules of the same size as that of the wavelength of the infrared light absorb the infrared light. However, the other wavelengths of light are passed through. The residual light hits the optical filter which absorbs another wavelength of light except for the exact wavelength that is absorbed by carbon dioxide. The infrared detector comprehends an exact amount of light which is not absorbed by the optical filter or the carbon dioxide molecules. This difference is proportional with respect to the carbon dioxide molecules present in the air inside the tube.

Gas Detection System

NDIR sensor is used extensively in the system and it comprises the infrared lamp, a thermistor and two thermopile channels. In order to save more power, it is best to prevent overheating the device. The lamp source is modulated with 50% duty cycle along with the frequency of 1 to 3Hz. The Reference channel and the Detector are directly connected to the inputs of the LMP91051. The filter capacitors are well connected with the common mode reference to each of the input in order to ensure low pass filtering. The external filtering option of LMP91051 is disabled and the pins A0 and A1 are made short internally within the chip. There is no need for high pass filtering because the internal offset DAC is taken to cancel all the offset errors in the signal chain. This makes the measurements faster compared to the traditional AC couple system. NDIR sensor has an internal thermistor connected to the resistor bridge and this is buffered with the amplifier. The entire system is powered off with the help of a single supply of the 3V.

Carbon Dioxide Detector Placement, Method and Settings

The NDIR system is well integrated into the infrared lamp and it is pulsed with 50% duty cycle which results in small 100’s uV RC waveforms. To bring about an overall improvement in measurement accuracy, the signals need to be amplified. There is the need for peak to peak waveform voltage for both the reference channel and the active channel when the comparisons are brought into the limelight.  There is a need for active DC offset adjustment which is essential to make sure that the output does not saturate and the signal chain offset errors are skilfully removed. It is necessary to achieve accurate sampling and for that multiple samples need to be used on each of the channels before you make the move of switching channels. The sampling needs to be synced perfectly to the lamp pulses so that the data is captured within the expected time which is relative to lamp switching. The same sample can be looked at over several lamp cycles to determine the noise performance.

Carbon Dioxide Gas Detector Performance

The functional features of LMP91051 were clearly demonstrated over the carbon dioxide concentration, the signal path gains, offsets and the frequency. Thermopiles used mainly in NDIR sensing have high internal resistance (~100 Kohm). Along with this, the signal path can get coupled with the 50/60Hz power main noise and then this will become noticeable in the entire setup of high gain application. Noise is always present in the signal path in the DC coupled system which without any filtering. In order to reduce the noise, a low-pass filtering needs to be added or the average filtering needs performance in the digital domain. In such a situation, the trade off is usually in case the cut-off frequency and that is too low, then the sensor signal might not have ample time for complete settlement.

The best and the most effective way to limit the wide band noise is by creating a low pass filter that has inherent source impedance. Thermopile sensors must have a source impedance which is up to 100 Kohms. The thermal noise has the ability to dominate the system noise. The right placement of capacitors from sensor outputs to the system common mode forms RC low pass filter and reduces the noise effects. In case of the verified 2Hz lamp frequency along with the thermopile source impedance which is of 85 Kohm, 6Hz low pass filter gets formed

FC = 1/(2π*R*C) = 1/(2π*85kohm*0.33uF) ~ 6Hz

An important point to be noted here is the lamp bias potential effect on the accuracy of the system. The light bulb glows because the current flows through the filament. The intensity of light emitted mostly depends on the lamp bias voltage and the light intensity, in turn, intensifies the effect of the thermopile output voltage. This is the primary reason why having a steady and constant light intensity is essential that can be over the entire sensor lifetime. Having a well regulated and clean power supply is instrumental in maintaining continuous emission of light. In order to understand the resolution, noise performance and span of the system, take note of the following measurement and calculation. PGA output captured with 12 bit A/D along with the voltage reference of 3V. A 6Hz low pass filter.

It is always essential to understand the mathematics and the mechanics of the Carbon Dioxide Gas Detectors so that the results you receive are high on accuracy.

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Know about the Different Types of Pressure Gauges

Different Types Of Pressure Gauges

Did you know that the instrument behind measuring air pressure Gauges is called a pressure or vacuum gauge? Well, yes many techniques have been invented to measure the air pressure. The pressure Gauges is one of them which defines and measures the air pressure. It is used to measure both high and low vacuum. There are different types of gauges available that measure different types of pressure depending on the intensity of the pressure. Earlier, mercury-filled glass instruments were invented to measure pressure. This is called a mercury gauge that was invented by Evangelista Torricelli. But, the presence of mercury restricted it from its wider usage and Know about the Different Types of Pressure Gauges.

 

pressure Gauges

  Pressure Gauges

I’ll give you a proper picture of the different types of Pressure Gauges that are identified through the following references. Keep reading below:

  • Pressure Gauges– This uses a reference of the atmosphere around the sensor. The reason behind this is the sensing element that has a deflection due to pressure Gauges change. A reference point is needed to know exactly what pressure is being measured. Some kind of vent is present in the pressure sensors. This vent can be built through a tube in the electrical connection.
  • Absolute Pressure– This is a combination of gauge pressure of the media with the pressure of the atmosphere. When the location changes, say as per the change of altitude, the atmospheric pressure also changes which compel the reference point to differ as well. If an absolute pressure sensor is used for eliminating the reference of varying atmospheric pressure.
  • Differential Pressure– It is slightly different than Pressure gauge or absolute pressure because it measures the difference between two medias. A true differential pressure sensor is used to measure the difference between two separate areas. For instance, the differential pressure is used to check the pressure drop from one object to another.
  • Sealed Pressure– It is not so common as compared to other three pressures. This uses a predetermined reference point that may not be vacuum. This allows for pressure management where the atmospheric pressure changes. For this, a venting is not needed as it doesn’t have a reference point.

The above-mentioned are the different types of pressure that are present in the world. This makes the use of pressure gauges according to the changing nature of the pressure.

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THERMO HYGROMETERS

Thermo Hygrometers

Thermo Hygrometers is used for measuring the humidity, temperature & has an integrated real time display. Do you know what humidity is? Humidity is the concentration of water vapour in the atmosphere and it is represented by a percentage. This instrument is the device with in-buillt sensors that measure humidity and temperature of the air. This reading is shown on the display of a Thermo Hygrometers.

 

Uses of Thermo HygrometersThermo Hygrometers

Thermo Hygrometers has more than one uses. Read below:

  • It helps in internal temperature stabilisationby displaying live temperature values
  • It scans the correct temperature conditions and protects you from deadly weather conditions.
  • It also helps in identifying the comparative humidity, the degree of dew point, temperature of the area and atmosphere.
  • Some Thermo Hygrometers monitors humidity within the house.
  • It can also preserve the foodstuffs from getting ruined by the humidity.
  • It can accurately display temperature , humidity & time in green rooms, pharmaceutical applications, clean rooms, machine rooms, etc.

Advantages of Thermo Hygrometers

This device is extremely helpful and helps you immensely in life. Read the advantages below:

  • It warns you regarding the amount of humidity that can be damaging to your system.
  • Thermo Hygrometers is used in special areas like public spaces, libraries and so on for ensuring right and cool environment.

Thermo Hygrometers is a vital device for measuring the humidity in the air. It provides alerts in case of dangerous weather conditions with its reading. It’s a must-

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