Tachymeter (watch)
A tachymeter or correct speedometer ( from Ancient Greek ταχύς tachýs "fast" and μέτρον métron " measure, scale " ) is in the watch industry, a scale on the dials or bezels of stopwatches or watches with stopwatch ( chronograph ). A total station is used to estimate at a fixed known path length (depending on the scale, for example 1 km) by means of the pointer on the basis of the speed scale, with the moving object or an operation takes place.
Operation
The tachymeter indicates the reciprocal value of the part of the hour that has passed since the second hand was on 12. With 30s for example, is 120 because 1/120 of an hour has passed. The magnitude of the tachymeter scale is 1 / h (pronounced " per hour " ), when multiplied by an arbitrary length is obtained, therefore, the change of this size per time, eg km / h ( kilometers per hour) or liters / h (liters per hour). So she takes the user to divide the measured variable ( distance, volume, etc. ) ( to come on unit per hour) by the measured time in seconds along with subsequent multiplying out at 3600 seconds / h.
Many total stations (such as where on the top two photos) assumed that the process to be measured for at least 15 seconds will take, but a maximum of 75 seconds. Therefore, slower processes, the scale division is mounted so that the fastest process at 3 clock ( after 15 seconds) is specified, however, still at eg 2 clock can be read off ( after 70 seconds). This slightly twisted scale division is confusing at first, since you initially oriented to the usual 12 - clock position. This rotation is due to the fact that too short measurement times, a significant measurement error can occur. If a process is measured by, for example, only 3 seconds and the measurement error is 1 second, there is an uncertainty of about 33 %. At 15 seconds of measurement time and 1 second measurement error, the inaccuracy is only about 6.7%.
Application Examples
Speed of a car: The speed of a vehicle can be determined easily by one (eg, 1 km) measures the time for a known distance on the tachymeter scale. If the distance traveled in 30 seconds, so the tachymeter scale indicates 120 (1 / h). The rate is therefore at a distance of 1km to 120 km / h Calculated exactly with Units:
Speed of a ship: To determine the speed of a sail boat, a buoy with a line of known length is thrown into the water during the trip. It will stop the time or the value on the tachymeter scale until tightens the leash and the buoy is pulled along. This Tachymeterwert is multiplied by the length of the leash and so gives the speed of the boat. If the length of the line in meters measured, we obtain the speed in meters per hour. If you want to know the wind speed in knots, ie nautical miles per hour, it must be converted accordingly. It is easier if the line has a length of eg 0.01 nautical mile ( NM ), ie about 18.5 meters, has. Then only 0.01 NM must be multiplied by the Tachymeterwert to obtain the speed in knots.
Speed of filling: For example, to determine the water consumption of a lawn sprinkler, one determines the Tachymeterwert for the filling of a pail with 10 liters of water. By multiplying the 10 liters with the Tachymeterwert you get the water consumption in liters per hour.
Pulse rate: When Nurses a fixed number is counted heartbeats. Counting starts when the second hand passes through the 12 - clock - or 6- clock position. The pulse rate can be read directly on the tachymeter scale. For the Nurses in the picture exactly 20 heartbeats are counted. A required counting time of 20 seconds corresponds to a pulse of 60/min. Reduces the counting time required to 15 seconds, the pulse is on 80/min.
Scale
The tachymeter scale is wristwatches often engraved on the bezel or printed, especially when it selectively outputs the clock with a rotating bezel for time determination. Not to confuse you a tachymeter with a slide rule bezel. The latter is provided with a logarithmic scale as a computer disc. The tachymeter scale does not need to be rotatably supported, then when you start counting, when the second hand reaches the 12 o 'clock position. Furthermore, it is not absolutely necessary to use a stopwatch function.
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