# Time base

The time base is a term used in measurement technology for a device for specifying a time span that is as precise as possible , also for generating time stamps for ongoing processes or for displaying the ongoing time within a time span. In addition to the central relevance of the time base in clocks , the term is particularly known in oscilloscopes for displaying the measured instantaneous values over time, which is shown in the horizontal axis.

## basis

Mechanical and analogue electrical time bases have largely been replaced since the 1970s by time bases using quartz oscillators or quartz oscillators and counting circuits (example: quartz watches ).

With simple quartz oscillators, such as those used as clock crystals , relative measurement uncertainties of less than 10 −5 are possible; By using suitable temperature controls in the form of a quartz furnace , the uncertainties regarding the temperature drift can be reduced by about three powers of ten. Precision time bases contain cesium elements that allow relative uncertainties in the range 10 −12 to 10 −13 . In specially set up laboratories such as the Physikalisch-Technische Bundesanstalt (PTB), a relative measurement uncertainty of 5 is determined when measuring time with atomic clocks e-15 reached.

## Applications

A known frequency of a clock generator is often used as a basis, which serves as a reference for further processes. For example, if a crystal oscillator has a frequency of = 10.0000 MHz, the period is = 0.100,000 μs. Any integral multiple of can be represented or measured by means of a counter circuit . ${\ displaystyle f_ {r}}$ ${\ displaystyle T_ {r} = 1 / f_ {r}}$${\ displaystyle T_ {r}}$

Time and frequency measurement

To measure an unknown duration, one counts how many periods fit into the unknown duration. If the count value is too large for a display, the frequency of the reference clock can be reduced with another counting circuit; see Digital Metrology # Counters for details . ${\ displaystyle T_ {x}}$${\ displaystyle T_ {r}}$

To measure an unknown frequency, one counts how many periods fit into a suitable time span. This time period is formed with a further counting circuit ; see frequency counter for details . The same applies to measurements of other variables that are defined by reference to a period of time, for example flow rate or rotational speed or speed. ${\ displaystyle f_ {x}}$${\ displaystyle T_ {r}}$

Positioning

The position determination in a navigation satellite system is based on a very precise time measurement (transit time measurement) and accordingly requires a very precise time base in the form of an atomic clock ( hydrogen maser in Galileo (satellite navigation) ) for signal processing .

Synchronization

Processes that have to run synchronously require a common time base that is accessible to all processes and that supplies at least one clock signal . An example is the timing for a processor or a bus (data processing) .

Measurement with an oscilloscope

The representation of the time in a given time period is a fundamental task in the oscilloscope and is there treated. The sampling of periodic signals at a very high frequency also places considerable demands on the time marking of the sampled values.

Here not only the electronic circuit is referred to as the time base, but also the scale set for the time display on the screen.

## Individual evidence

1. Reinhard Lerch: Electrical measurement technology: analog, digital and computer-aided processes. Springer Vieweg, 6th edition 2012, p. 395
2. Horst Germer, Norbert Wefers: measuring electronics, volume 2: digital signal processing, microcomputers, measuring systems . Hüthig, 1986, p. 73 ff
3. Ludwig Borucki, J. Dittmann: Digital measuring technology: An introduction. Springer, 1966, p. 68
4. Holger Flühr: Avionics and Air Traffic Control Technology: Introduction to Communication Technology, Navigation, Surveillance. Springer Vieweg, 2nd ed. 2012, p. 121
5. Hartmut Ernst: Basics and Concepts of Computer Science: An introduction to computer science based on the fundamental principles. Springer, 2002, p. 160