As you agree any Automation involves substitution of human judgment by a device. The intelligence built into the device should be such that its decision must be almost nearer to a rational human judgment by a knowledgeable person in the field. In a Nature Switch the judgment is based on infrared sensor. Consequently the sensor while sensing the solar radiation will not sense the light from most of the normally used outdoor fitted artificial light sources like LPMV, HPSV, HPMV etc since their emission in the infrared spectrum is very negligible for all practical purposes. The ordinary incandescent lamp is the only exception, which in any case is not being used, in large numbers due to their inefficient energy conversion factor. The infrared sensor is also immune to moon light.
The field of view is another important critical design feature, which will determine the normal field sources that are accepted and those that are not accepted. Nature Switch is provided with a carefully selected field of view thus making the Nature Switch not to receive any light emitted by ground-based sources like automobile light or a torchlight etc. Even the light emitted by a lamp fitted to a post on which the Nature Switch is installed will also not reach the sensor. This FOV coupled with the spectral immunity and the level of the signal at 60 lux will for all practical purposes make the Nature Switch to have a highly stable decision making capability regarding the transition from day to night and from night to day. This decision will invariably depend only on natural solar radiation and not the artificial light sources. The near total uniformity of the sky in the post sunset and pre sunrise situation will facilitate the installation of the Nature Switch in any direction like east, west, north or south without any restriction.
The infrared sensor selected for Nature Switch is highly stable in the long run and will not exhibit calibration drift and will be linear up to the point of saturation and will be immune to humidity and temperature. The stability of the device is proved and is assured with the above sensor selection.
The light level selected for judging the switching ON is 60 lux and for switching OFF it is 10 lux. As the generally aimed Illuminance level in most of the outdoor areas as per BIS standards is about 30 lux, the Nature switch will switch ON the lamps on sensing that the natural light level has gone below 60 lux for a continuous period of 30 seconds. With this the artificial lamps are switched ON at the appropriate time. For switching OFF, a level of 10 lux is appropriate since human visibility will build to a satisfactory level even at 10 lux in the early Dawn. The model with timer will switch OFF the load after the selected duration instead of waiting till dawn.
One may have a feeling that clouds, rain, fog, mist etc will make the Nature Switch to misjudge the ambient levels and leads to switch ON even during the day. Nature Switch is constructed in such a way that the sensor is sealed in a container to the standards of IP 65. The presence of cloud, rain, fog, mist etc during the time when the sun is above the horizon will not make the ground Illuminance fall below 60 lux. This can happen only after the sunsets or before the sunrise. Consequently no erratic switching will occur in Nature Switch.
The actual timing of switching should logically be decided based on a dynamic situation, which is influenced by atmospheric conditions, which may vary not only by seasons but also on each day. The timing based switches known as timers cannot really address the issue in view of their fundamental limitation of going by a preset time which may or may not meet the actual field requirements. The infrared sensor based Nature Switch with total immunity but capable of responding to the dynamic variations is the most appropriate and unique solution.
There may be a genuine feeling that dust present in the general atmosphere and the high degree of the same in busy streets, factories etc will get accumulated on the sensor window and will make the switch to behave erratically. The other devices tried out in the past were having design limitations with regard to dust prevention. Nature Switch is designed is such a way that the sensor window is part of a vertical wall and the material used for window construction is having anti static properties to repel the dust particles. The normal forces of wind and water will remove the small layers and so the device performance will not drift drastically on account of dust.
The other question usually raised is the effect of fixing the device under the shade of trees and sunshades. While the tree will block a major portion of sunlight in the midday it's effect in the dawn and dusk times will be very less in view of the fact that light will be reaching from all directions of the sky almost with the same intensity. The Nature Switch will switch ON or switch OFF the lamps only when we do not find any shade of a tree. But however a tree shade will have an impact in terms of a slight shift in the timing of operation of the device. The real difference in terms of time may be as low as 1 second to a high of 5 minutes.
The suggested height for fitment is 6 feet from the ground so that the normal pilferages and unwanted handling by passersby will be eliminated. This will also make the sensor not to receive the mud splashing from a moving traffic in the rainy season.
The general failure of electronic devices occurs due to many factors like water, corrosion, high voltage, thermal damage, component failure etc. Nature Switches are housed in an insulated molded engineering plastic container sealed to IP 65. This is to ensure that no atmospheric contaminants like moisture; corrosive chemicals etc will not enter the circuit area. The internal thermal generation is as low as less than 1 watt and the same is carried away to the ambient by the metal terminals. Each of the electronic components is capable of performing up to 80 degrees centigrade. The thermal elevation at the hottest spot in the circuit will be a maximum of 20 degrees. So the device can perform continuously in an ambient of up to 60 degrees centigrade while the highest open-air temperature ever recorded on the surface of the earth is known to be only about 54 degrees.
The Nature Switches do not have a transformer, which is a cause for many known failures, and a continuous voltage of even up to 440 also cannot damage the circuit. Surges and spikes in the mains voltage are suppressed with specially chosen varistors. The overload trip and latch mechanism will protect the device and also the load circuits from high load currents, which can occur due to many factors beyond the control of, even the user. The device is also provided a special provision of over voltage detection and trip and auto reset. Similarly low voltage also is detected. The device will be stable and can perform in a voltage range from 120 to 440 Volts AC though the load is tripped at below 150 volts and above 280 volts for protection.
The device was tested at full load of 16Amps for 5000 cycles, which means an operation for 5000 days, which is about 14 years. The sparks across the power switch contacts at the time of switch OFF is minimized with special components.The overload trip circuit trips the over current on the power switch automatically. The current is measured continuously by a non-series sensor, which is calibrated for reliability.
The operational state of the Nature Switch should always be clear to the user. This is facilitated by an LED, which changes its color as per the state. Green, Amber and Red are the three states of the LED. LED also flashes for in different colors to indicate that the Nature switch has tripped the load and the reason for tripping is indicated by the color of the flash of the LED.
The construction facilitates an easy installation with the help of two screws. The total weight is less than 400 grams, which can be easily suspended. The terminal box is designed to ensure easy access and at the same time to provide isolation. The terminal box is molded by using flame retardant grade plastic materials with good mechanical properties. A neoprene rubber based shroud will prevent the insects like ants etc from coming in contact with the live cables. The SWADEEP 02-EC is designed to be installed as an integral system and the product comes with all the needed fixing brackets etc. SIGN SWITCH is designed to be installed at the time of manufacture of the signage itself.
Nature Switch is intended as a direct substitute to an existing manual switch. It does not need a contactor if the connected load is less than 16 Amp. If the load is more, the same can be handled with the help of a contactor like all the present timer based installations. If a contactor is used in a single-phase installation of more than the rated load or in a three-phase installation of any load the Nature Switch will only drive the coil of the contactor, which will handle the actual lamp load.
We wish to conclude by saying that the Nature Switches were designed keeping in view the field requirements and they have proved their reliability and utility.