Why are 3D printers so expensive?
The PrintrBot Play is $399 and the Simple Metal is $599. The M3D Micro is $349. The DiVinci 1.0 is $499 and the 2.0 $649. Newmatter MOD-t is $249. A solidoodle 4 is $599 You'd be hard pressed to build these with off-the-shelf parts at these prices, so categorizing them as "so expensive" really isn't fair. There's a lot of technology, machining, custom parts, etc. that go into these devices and the hobbyist groups are pretty much selling them for a minimal profit. The more "turnkey" devices like a Makerbot, Ultimaker, etc. are more consumer focused and they've had to make them extremely "idiot proof". They also have to accept significantly more risk because the target audience is generally not a hobbyist or experimenter, but someone with a job to get done who's going to be demanding reliability and support on an ongoing basis. The way to pay for that support staff, extensive testing and engineering support is to charge more for the product. On the really high end, you've got products that essentially are loaded with sensors, feedback loops, lots of self-tuning software and monitoring and much higher precision components (not to mention a boatload of calibration either done at the factory or by an engineer who delivers/installs it). You pay a premium for a device that's essentially guaranteed to produce a certain quality of print no matter what you throw at it. Fundamentally, they're not that much different from the low end devices, but the engineering, manufacturing and testing is far more precise, the components are higher tolerance and there are often additional components and/or subsystems that ensure that the device will perform (all very similar to the differences between a budget compact car and a performance sports car) Finally, prices tend to shoot up as the print area increases. There are the costs of the raw materials, equipment to handle the larger parts, storage and shipping costs, etc. But, more importantly, as the size increases, variations in manufacturing, components, calibrations, etc. become far more evident and have a greater impact on print quality. The expectation is normally that you want to maintain the same resolution and print quality, but across a much larger object. That scalability doesn't come cheap. What may be an insignificant variation in a stepper motor or the linearity of a travel rod on a 4x4x4 printer can become a show stopper on an 8x8x8 unit.
Why is the linearity of a sensor a desirable feature?
First of all multiply and divide are more basic operations compared to square root and this might imply that you need much more complex(and expansive) electronics to convert the signal into the actual measure. Then the inverse conversion is not unique, i mean that -X produces the exact same Y of +X... otherwise if a negative input produces a negative output could also give problems(remember that square root of a negative number don't exist in real numbers). Another problem is that small measures give infinitesimal signals while large measures give enormous signals. Imagine for exampre your sensor output is in volts, if the measure is 0.1 the transducer output signal would be 0.01V, while if the measure is 10 the output signal would be 100V....if the measure is 100 the output would be 10000V. this is quite inpractical.... Actually a sensor that sometimes is better than linear could be logaritmic cause "amplifies" small measures and attenuates higher measures(0.1 would be -1, 1000 would be 3, 1000000 would be 6) and allows you to manage both very small measures and very large measures at the same time.... the quadratic sensor does exactly the opposite. The drowback of logaritmic sensors is that they also need more complex devices to work with compared to linear that are the easiest to manage. this drowback is sometimes small compared to the advantages of a logaritmic sensor but it would be a nonsense with the disvantages of a quadratic sensor.
What´s the difference between 1 Stage und 2 Stages OTA?
The operational transconductance amplifier provides essentially a voltage controlled current source with relatively high impedance in the single-stage case. Think of the two-stage like a Darlington pair, it will increase the gain and reduce the output impedance…See this cool lab at the Analog site. I'd like to try it myself, but, y’know, “day job” and kids. ;^)Activity: 2 Stage CMOS OTA
Why is mercury used in thermometers?
Liquid in glass thermometers are the cheapest kind of thermometer, and are also easy to use. Mercury is easily the best liquid to use, for 5 important reasons.1. It is very reflective, so it's easy to see and to read accurately.2. It doesn't wet the glass, so you don't get inaccurate readings if the temperature is falling.3. It is a metal, so it's a good conductor of heat. This means that it reacts quickly to changes of temperature.4. It expands evenly with temperature, so a linear scale can be used with quite a high degree of accuracy.5. There's a large range of temperature for which it is a liquid. However, it freezes at - 39 Celsius, so Mercury cannot be used below this temperature. It boils at 365 Celsius, which is high enough for most purposes.Colored water is no good because it's a poor conductor, it wets the glass, it expands unevenly with temperature, and there is only a limited range of temperatures for which it is a liquid, 0 - 100 Celsius.Cheaper, and for temperatures below -39 C, colored ethanol is used. This freezes at - 144 C, but it boils at 78 C, making it of no use at high temperatures. It expands quite evenly with temperature, but otherwise it has the same defects as water. To get an accurate reading, it should be vertical and you have to give it plenty of time before you take a reading.