Mar 31

MEASURING INSTRUMENTS FOR SOLAR POWER SYSTEMS

While performing on numerous types of solar power systems, it’s extremely necessary to grasp the reading, regarding the radiation emitted from the sun, by its measuring devices and recording devices. The radiation of sun to the earth’s surface consists of 2 components like direct radiation and diffused radiation. Different types of solar measuring instruments, e.g., sun shine recorder, pyrheliometer, shading ring pyranometer are needed to measure these live radiations which offer the output in mV and need to be regenerate into correct units by multiplying with their calibration factors. These outputs are then recorded by numerous devices obtainable on the market.

1.  PYRANOMETER

Pyranometer is very sensitive instrument that measures the intensity of total radiation received at earth’s surface over a hemispherical field view.

01-pyranometer - solar measurement equipment

DESCRIPTION:

Typical pyranometer, primarily it consists of a thin blackened surface, that is encircled in two concentrically hemispherical glass domes, so as to defend it from wind, rain and dirt. This surface is connected to a multi junction thermopile and is supported within a comparatively huge well polished case. The hot junctions (input) of this thermopile lie on the ring that is located along the side (upper) of the sensing element. Whereas, ‘passive’ are cold junctions which are situated in such away that they do not receive any radiations.

01-pyranometer-sensor - measurement instruments

INSTALLATION:

It is essential for the pyranometer to be mounted in the open, in such a position that there’s no obstacle to impede sun rays in all seasons between sunrise and sun set. An acceptable platform or pillar on the flat roof of the building with no tall tree or building obstructing the radiation from any part of the sky would be the most effective one.

01-pyranometer-solar power measurement system

CALIBRATION:

Pyranometer are usually calibrated against standard pyrheliometers. A standard customary technique has been forth within the annals of the international geophysical year 1953. Which needs that, readings to be taken at the time of clear skies, with the pyranometer shaded and pyranometer unshaded at an equivalent or constant time, once readings are taken with pyrheliometer. Shading is suggested to be accomplished by means of disc held at 1m from the pyranometer, with the disc simply large enough to shade the glass envelope. The calibration constant is the ratio of the difference within the output of the shaded and unshaded pyranometer to the output of pyrheliometer and cosθz, the angle of incidence of beam radiation on the horizontal pyranometer. Care and precision / exactitude are needed in these calibrations. It’s potential to calibrate the pyranometer against a secondary standard pyranometer. The direct comparison of the measuring device (secondary) and field instrument (primary) is additionally created to effort the calibration constant of the spherical instrument.

01-pyrheliometer - solar radiation measurement

2. SUNSHINE RECORDER

The hours of bright sunshine, (i.e. through that the solar disc is visible) which is used to estimate the long term run of average solar radiation. The instrument accustomed to collect such data is termed as sunshine recorder.

01-Sunshine Recorder - solar radiation measurement - radiation measurements

DESCRIPTION:

It consists of glass sphere mounted in a brass bowl with a groove for holding the recorder cards. The spherical glass once exposed to the sun produces its image on the alternative facet / side that burns a trace on the cardboard, which are mounted concentrically with the sphere. As the sun moves across the sky, so as the position of the spot across the card. Once the sun is obscured, because of clouds etc., the trace is interrupted. Within the end of the day the overall length of the traceless gaps provide the duration of bright sunshine. The instrument is commonly mounted on a marble base, the bowl being supported within a semi circular brass bar. The sphere is controlled at 2 ends by brass screws that match into cups fixed on the sphere. The bowl has 3 sets of grooves for taking 3 sets of cards, long spline for summer, short spline for winter and straight cards at equinoxes.

01-Sunshine Recorder - solar radiation measurement

INSTALLATION:

As just in case of pyranometer, the sunshine recorder ought to be installed at an area wherever there’s no obstruction to the sun.

OPERATION:

Once the instrument has been setup and properly adjusted, it needs very little attention beyond changing the cards everyday. While inserting the cards, care should be taken to make sure that midday line on the card coincides precisely with the noon mark on the bowl.

3. ANEMOMETER

Anemometer may be a van-type digital instrument used to measure the air speed & air velocity in meter per second. Its variation of range is 0-15 m/sec. The operation of vane-type gauge is as follows.

DIGITAL TEMPERATURE INDICATOR:

The most common electrical method of temperature measurement uses the thermo-electric sensing element, which also referred as the thermocouple junction. The construction of the thermocouple junction consists of two wires of various metals twisted and brazed or welded in conjunction with every wire coated with insulation. The variation of range is of 0-16000C.

01-anemometer-hand held - wind speed meter

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Jan 28

Making of Ultrasonic Weld:

01-ultrasonic welding process

Although the theoretical method of manufacturing an ultrasonic weld is uncomplicated, the interactions of the varied weld parameters are vital and may be understood. When manufacturing an ultrasonic weld, there are 3 primary variables that interact;

They are:

TIME the period of applied ultrasonic vibration

AMPLITUDE the longitudinal displacement of the vibration

FORCE the compressive force applied perpendicular (normal) to the direction of vibration

Power needed initiating and maintaining vibration (motion) throughout the weld cycle will be defined as:

P = F x A

Where:

P = Power (watts)

F = Force (psi)

A = Amplitude (microns)

 

Force = (Surface Area of the Cylinder) X (Air Pressure) X (Mechanical Advantage)

 

Energy is calculated as:

E = P x T

Where:

E = Energy (joules)

P = Power (watts)

T = Time (seconds)

Thus the complete ‘Weld to Energy’ process would be defined as:

E = (F x A) x T

A well designed ultrasonic metal welding system can compensate for normal variations within the surface conditions of the metals by delivering the required energy value. This is often achieved by permitting time (T) to regulate to suit the condition of the materials and deliver the required energy.

01-ultrasonic welding machine - high frequency welding

How Ultrasonic Welding Works:

Step 1: The parts to be welded are placed into a locating holder

Step 2: The ultrasonic tool descends to apply a clamping pressure between the weld parts.

Step 3: The tool then vibrates at a frequency 1 – 40 KHz. (The weld parts are thus scrubbed together under pressure causing surface oils and oxides to be dispersed)

Step 4: The base metals are then mechanically mixed causing a metallurgical bond between the parts. The parts are immediately welded. There is no hold time or curing time.

In Ultrasonic welding electrical power supply is applied to a Transducer at a frequency of 50 to 60 Hz, into a high frequency electrical supply operating at 20, 30 or 40 KHz. Here transducer converts electrical energy into mechanical energy. This electrical energy is supplied to the converts, which converts to mechanical energy at ultrasonic frequencies.

01-ultrasonic transducer - ultrasonic generator

The vibrating energy is then transmitted through the booster that will increase the amplitude of the acoustic wave. The acoustic waves are then transmitted to the horn. The horn is an acoustic tool that transfers the vibrating energy directly to the components being assembled, and it additionally applies a welding pressure. The vibrations are transmitted through the workpiece to the joint area. The parts are “scrubbed” together under pressure at 20000 cycles per second. Here the vibrating energy is converted to heat through friction this then softens or melts the thermoplastic, and joins the components together. As the atoms are combined between the components to be welded, a real metallurgical bond is made.

01-ultrasonic welding horn

Welding Temperature Achieved:

Ultrasonic welding produces a localized temperature rise from the combined effects of elastic hysteresis, interfacial slip and plastic deformation. The weld interfaces reach roughly 1/3 the temperatures required to melt the metals. Since the temperature doesn’t reach the melting point of the material, the physical properties of the welded material are preserved. As the ultrasonic welding method is an exothermic reaction, as welding time will increases so does weld temperature.

The ultrasonic welding process has the advantage that since no bulk heating of the work pieces is involved and there is no danger of any mechanical or metallurgical bad effects. Although metals have up to 2.5 mm thick have been welded by this process. It is used mostly for welding foils. This process is suitable only for thermoplastics with the exception of thermosetting resins and Teflons. The process can be used on a variety of metals including the refractory metals. Even dissimilar metals can be welded because there is no fusion. The process can also be used on temperature sensitive materials because temperature rise is limited.

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