Depreciation Problems engineering economy
enginnering economy
ME BOARD APRIL 1998
A machine has an initial cost f P50000 and a salvage value of P10000 after 10 years. What is the book value after five years using straight line depreciation?Ans. P30000
ME Board April 1998
An asset is purchased for P500000. The salvage value in 25 years is 100000. What are the the depreciations in the first three years using straight line method?Ans. P48000
CE Board Nov 1997
The cost of equipment is P500000 and the cost of installation is P30000.If the salvage value is 10% of the cost of equipment at the end of 5 years, determine the book value at the end of the fourth year.use straight line method.Ans. P146000
ECE Board Nov 1999
A machine costs P8000 and an estimated life of 10 years with a salvage value of 500. What is the book value after 8 years using straight line method?Ans. P2000
An engineer bought an equipment for P500000. He spent an additional amount of P30000 for installation and other expenses. The salvage value is 10% of the first cost. If the book value at the end of 5 years will be 291500 using straight line method of depreciation, compute the useful life of the equipment in years? Ans 10 years
ME Board April 1992
A unit of welding machine cost P45000 with an estimated life of 5 years.Its salvage value is P2500 find its depreciation rate of sinking fund method. Assuming that will deposit the money to a bank giving 8.5%. Solve for the depreciation.Ans. 7172.54
EE board April 1980
A equipment cost p10000 with a salvage value of P500 at the end of 10 years. Calculate the annual depreciation by sinking fund method at 40% interest.
CHE Board Oct 1980
A 110000 chemical plant had an estimated life of 6 years and a projected scrap value of P10000. After 3 years made it a total loss . How much money would have to be raised to put up a new plant costing P150000, if a depreciation reserved has been maintained during its 3 years of operation by sinking fund method 6%.104359
ME board Sept 1971
A dump truck was bought for 30000 six years ago. It will have a salvage value of P3000 four years from now. It is sold now for P8000. What is the sunk cost if the depreciation method used is sinking fund method at 6%. 7712
CE Board 1999
The corporation purchased a machine for P1 million. Freight and installation charges amounted to 3% of the purchased price. If the machine shall be depreciated over a period of 8 years with a salvage value of 12% of the first cost. Determine the depreciation charged during the 5th year using the SYD method.100711
ME Board April 1998
An Asset is purchased for P9000. Its estimated life is 10 years, after which it will be sold for P1000. Find the book value during the third year if SYD depreciation is used.5072
ECE Board 1998
ABC corporation makes its policy that for every new equipment purchased the annual depreciation cost should not exceed 20% of the first cost at anytime without salvage value. Determine the length of service if the depreciation used is the SYD method.9 years
ME board April 1996
An asset is purchased for 120000. Its estimated life is 10 years after which it will be sold for 12000. Find the depreciation for the second year using the SYD method.17673
Infrared Sensors
Infrared proximity sensorsInfrared proximity sensors work by sending out a beam of IR light, and then computing the distance to any nearby objects from characteristics of the returned (reflected) signal. There are a number of ways to do this, each with its own advantages and disadvantages:
Reflected IR strengthYou could build a simple IR proximity sensor out of essentially just an IR LED and IR photodiode. This simple sensor, though, would be prey to background light (i.e., your IR "receiver" would be responding to naturally present IR as well as reflected IR).
Modulated IR signalA better solution would be to modulate your transmitted IR (i.e., to send out a rapidly-varying IR signal), and then have the receive circuitry only respond to the level of the received, matching, modulated IR signal (i.e., to ignore the DC component of the received signal, and only trigger off the AC component). This method, though, is still at the mercy of the characteristics (in particular, IR reflectance) of the obstacle you're trying to sense.
Steve Bolt has a nice circuit to do this here.
TriangulationThe best way to use IR to sense an obstacle is to sense the angle at which the reflected IR is returned to your sensor. By use of a bit of trigonometry, you can then compute distance, knowing the location of your transmit and receive elements. Needless to say, this isn't a simple sensor to build yourself.
You're probably money ahead by just buying an IR proximity sensor with this logic built in. One I particularly like is the Sharp GP2D15 IR Ranger. It has a built-in detection range of 24 cm (this keeps its cost, and the complexity of your interface circuitry down), is reasonably priced, and is available from Acroname. Acroname also has an interesting article covering the operation and utilization of all the impressive Sharp IR sensors here.
The GP2D15 interface is 3-wire with power, ground and the output voltage (the sensor outputs Vcc when it sees something at 24 cm distance); it requires 4.5 - 5.5 V power for operation, and eats about 50 mA of current as long as it is powered. So its advantages are (1) its simple interface, and (2) easy, reliable sensing of obstacles at a distance. Its disadvantages are (1) its requirement for 5 V power, and (2) its requirement for 50 mA of current regardless of whether anything is being sensed (neither of these recommend this sensor for solar-powered 'bots).
If your BEAMbot's circuitry has provision for a "touch-switch" contact sensor, the GP2D15 can easily be used instead, with the addition of an NPN transistor:
Acoustic proximity sensorsOne oft-used method (at least on larger, pricier 'bots) of avoiding hazards is via sonar ranging. Here, acoustic signals ("ping"s) are sent out, with the time of echo return being a measure of distance to an obstacle. This does, unfortunately, require fairly accurate timing circuitry -- so acoustic sensors really require a processor of some sort to drive them. Also note that acoustic sensing essentially requires the use of commercial sensors, there's no real way to "homebrew" something from scratch.
The most common acoustic proximity sensor is the kind used in polaroid cameras. For details on these, I'll refer you to the Acroname site's "Polaroid Sonar Ranging Primer."
There's now also a "new kid on the block" -- the Devantech SRF04 UltraSonic Ranger. Acroname sells it (see their page on it here), and "Tech Geek" has a review on it here. This guy costs about twice what the Sharp IR sensors cost, but has a much wider range of sensing; it costs far less than the Polaroid acoustic rangers, is easier to interface, and draws less power.
Capacitive proximity sensorsYour 'bot can also sense its distance to objects by detecting changes in capacitance around it. When power is applied to the sensor, an electrostatic field is generated and reacts to changes in capacitance cause by the presence of a target. The main disadvantage to this sensor (often called a capaciflector) is that its usefulness is dependent on properties of the obstacles it is sensing (namely, their dialectric constant). The higher the dielectric constant (say, water), the more sensitive a capacitive sensor is to that target. The sensing distance depends on the dielectric constant of the target and the surface areas of the probe and the target.
I go into more depth on this interesting sensor elsewhere.
Inductive proximity sensorsAnother method for sensing distance to objects is through the use of induced magnetic fields. The primary problem with this method is that it is largely confined to sensing metallic objects.
Based on a simple basic Idea, this proximity sensor, is easy to build, easy to calibrate and still, it provides a detection range of 35 cm (range can change depending on the ambient light intensity).This sensor can be used for most indoor applications where no important ambient light is present. For simplicity, this sensor doesn't provide ambient light immunity, but a more complicated, ambient light ignoring sensor should be discussed in a coming article. However, this sensor can be used to measure the speed of object moving at a very high speed, like in industry or in tachometers. In such applications, ambient light ignoring sensor, which rely on sending 40 Khz pulsed signals cannot be used because there are time gaps between the pulses where the sensor is 'blind'...
The solution proposed doesn't contain any special components, like photo-diodes, photo-transistors, or IR receiver ICs, only a couple if IR leds, an Op amp, a transistor and a couple of resistors. In need, as the title says, a standard IR led is used for the purpose of detection. Due to that fact, the circuit is extremely simple, and any novice electronics hobbyist can easily understand and build it.
Object Detection using IR light
It is the same principle in ALL Infra-Red proximity sensors. The basic idea is to send infra red light through IR-LEDs, which is then reflected by any object in front of the sensor.
Then all you have to do is to pick-up the reflected IR light. For detecting the reflected IR light, we are going to use a very original technique: we are going to use another IR-LED, to detect the IR light that was emitted from another led of the exact same type!This is an electrical property of Light Emitting Diodes (LEDs) which is the fact that a led Produce a voltage difference across its leads when it is subjected to light. As if it was a photo-cell, but with much lower output current. In other words, the voltage generated by the leds can't be - in any way - used to generate electrical power from light, It can barely be detected. that's why as you will notice in the
schematic, we are going to use a Op-Amp (operational Amplifier) to accurately detect very small voltage changes.
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