Test Watches Silent Approved ( STW or QSTW)

A silent test watch is a portable electronic timepiece used to calibrate other watches and clocks.

It is often referred to as STW (silent test watch), QSTW, or service watch.

This device is normally carried by an official in the military or intelligence agencies while on duty; its function is not for the user’s personal use, but to be available when needed in the field.

The STW was invented as a result of older methods being insufficiently accurate and too bulky for comfortable carry. It consists of either one battery-powered quartz oscillator running at a known, stable frequency (such as 32 kHz) with the addition of a voltage-controlled crystal oscillator that operates over a much larger range, up to several GHz. These provide a reference frequency and timing signal, respectively, which can be used to adjust the accuracy of other clocks or watches by comparing them with it. The STW operates continuously in order to maintain its accuracy, while other timepieces are typically used for short period measurements (e.g., seconds) connected to an external source such as a laboratory standard.

The STW is sometimes called a “beats per second” instrument because its output pulses at a known rate that is determined by the frequency stability of the 32 kHz oscillator.

The use of GPS receivers instead of internal clock sources has led some governments to discontinue their use; others still issue them as general-purpose equipment for military personnel. In September 2011, the U.S. Air Force announced that they were decommissioning their STWs; the units have been replaced by GPS-aided devices, which do not require periodic calibration.

A silent test watch is a portable electronic timepiece used to calibrate other watches and clocks or to generate known timings for tests of equipment under development. All modern versions use at least one quartz crystal oscillator synchronized with an external standard such as WWV from Fort Collins [3]. Its function is not for the user’s personal use, but to be available when needed in the field. This device is normally carried by an official in the military or intelligence agencies while on duty; its function is not for the user’s personal use, but to be available when needed in the field.

It is often referred to as STW (silent test watch), QSTW, or service watch. This device is used for calibration, time transfer, and frequency stability checks on equipment including clocks for commercial, industrial, and scientific purposes; atomic clocks; pneumatic transport delays in telephone exchanges; quartz-controlled transmitters for radio navigation beacons (LORAN); accelerometers; inertial guidance systems.

The STW was invented as a result of older methods being insufficiently accurate and too bulky for comfortable carry. It consists of either one battery-powered quartz oscillator running at a known, stable frequency (such as 32 kHz) with the addition of a voltage-controlled crystal oscillator that operates over a much larger range, up to several GHz. These provide a reference frequency and timing signal, respectively, which can be used to adjust the accuracy of other clocks or watches by comparing them with it. The STW operates continuously in order to maintain its accuracy, while other timepieces are typically used for short period measurements (e.g., seconds) connected to an external source such as a laboratory standard.

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A silent test watch has one or more quartz crystal oscillators that must be accurate within parts per million; their calibration is checked by using them together with an ionization chamber-based frequency standard like NIST-F1. The whole assembly makes up the STW’s “spec”. Various options vary the functionality: besides the basic timekeeping modules, a user may also select frequency output or pulse-per-second (PPS) output, voltage control to drive other clocks and timing devices, auxiliary lighting for low-visibility use. The STW is sometimes called a “beats per second” instrument because its output pulses at a known rate that is determined by the frequency stability of the 32 kHz oscillator.

The 1970s saw their proliferation among military users; since then they have been widely issued as general-purpose instruments. By 1994 silent test watches were being phased out in favor of GPS receivers with special adapters for time transfer applications: all modern ones are battery-powered quartz oscillators synchronized with an external standard such as WWV from Fort Collins. A time transfer application only requires that the signals remain in sync for about 30 seconds; STWs need to be able to run continuously for a minimum of three years without adjustments.

The U.S. military issues them to soldiers and intelligence officers wherever they may be in the world, whether on assignment or as part of their uniform or equipment. The devices are sometimes called a “beats-per-second instrument” because their output pulses at a known rate that is determined by the frequency stability of the 32 kHz oscillator. Its function is not for the user’s personal use but to be available when needed in the field. It differs from other quartz crystal watches such as those issued to pilots because it must remain accurate to within a few parts per million. The watches have been used for calibration, time transfer, and frequency stability checks on equipment including clocks for commercial, industrial, and scientific purposes; atomic clocks; pneumatic transport delays in telephone exchanges; quartz-controlled transmitters for radio navigation beacons (LORAN); accelerometers; inertial guidance systems.

The STW operates continuously in order to maintain its accuracy,[6] while other timepieces are usually used for short period measurements. Thus an army soldier tracks the arrival of convoys or the start of enemy raids with a stopwatch, whereas his own watch’s main function is to make sure it has not drifted too far from Coordinated Universal Time. Normally kept in a secure area, the watches can be rechecked against each other or an outside standard periodically. A common problem occurs when a soldier forgets to reset his watch after going on daylight saving time. Some STWs have backup gas-discharge tubes that provide some illumination for military operations in darkness and/or complete darkness.

The idea of wristwatch precision metrology goes back at least to the 1930s: one early example is a pendulum clock with an optical sensor (designed by Arthur Cook, Jr.) used as part of an experiment at Caltech’s Table Mountain Observatory.

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