Absolute Standoff 2

[Tina Popielarczyk]

Policeconverged on the area of Broad and North Mathilda Street around 11 a.m. after shots rang out while Allegheny County Sheriff's deputies were at a home to serve an eviction notice to the suspect, later identified as William Hardison, Sr.

Allegheny County Sheriff Kevin Kraus said the gunman was shooting out of the first- and second-floor windows and through the wall. Deputies returned fire and "engaged in a pretty significant gun battle," Kraus said. He said there was a "lengthy" gun battle before SWAT officers arrived and stabilized the scene.

Thousands of rounds of ammunition were fired at police and Martin Nichols, who lives next-door to where the shootout occurred, says that Hardison was a menace who was squatting on the property and was terrible to neighbors in the area.

"There were holes all through my walls," Nichols said. "There was dust literally everywhere. It didn't even look like a home at that point. The front of my house was overall okay. I will say that the inside, as soon as you walk through the front, it looked like an absolute warzone."

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RESOLUTE outperforms all other absolute encoders that are designed for UHV environments. Capable of 1 nm resolution and up to 100 m/s, RESOLUTE provides a specification that breaks new ground in encoder technology.

RTLA30 is a low profile stainless steel tape scale featuring 30 m pitch absolute scale code. It is accurate to 5 m/m and available in lengths up to 21 metres. Two mounting options are available, both of which allow independent thermal expansion and tape scale convenience.

RESOLUTE UHV takes Renishaw's revolutionary absolute encoder technology and delivers it in a readhead that is suitable for use in Ultra-High Vacuum conditions up to 10 -9 Torr. The new range of RESOLUTE UHV encoders are constructed from clean residual gas analysis materials (RGA) making them suitable for high performance, semiconductor and scientific applications.

RESOLUTE UHV does not follow the conventional technique of using dual tracks side-by-side (one incremental, one absolute) which inherently suffers de-phasing problems when small amounts of angular misalignment are introduced. Instead, this absolute encoder features a single track, optical absolute scale, combining both the absolute position and embedded phase information into one single code. This technology provides RESOLUTE UHV with far wider set-up tolerances (yaw tolerance 0.5) for quick and easy installation and superior long-term reliability, even if the motion axes settle or move over time. To further aid installation and diagnostics, there is an integral set-up LED on the readhead.

RESOLUTE encoder readheads (marked with the ADT symbol) are compatible with the Advanced Diagnostic Tool ADTa-100 and ADT View software. They provide comprehensive real-time encoder data feedback to aid more challenging installations and diagnostics. The intuitive software interface can be used for:

Absolute encoders are rotary encoders that measure angles, convert this information into electrical signals and output them as absolute values. The use of electronics to process the measured value distinguishes them from potentiometers, which also provide absolute values but are passive components without integrated electronics. Absolute encoders have a fixed reference point for angle measurement to which the output value is always referenced. The principle of an absolute encoder is fundamentally different from that of an incremental encoder, for example, where only angle changes (relative values) are transmitted by the encoder.

Absolute encoders are divided into two categories according to the angular range to be measured. Encoders that measure angles over several revolutions are called multiturn encoders, and encoders that measure angles up to 360 are called singleturn encoders.

Absolute encoders offer a wide range of options for displaying the measured angular values as an electrical signal function at the output. The electronics of many encoders are programmable, allowing the output waveforms to be customized. The following example shows the standard factory programming of an analogue absolute encoder:

The encoder is programmed in the CW direction of rotation with an output signal of 0...10 V (when the shaft rotates clockwise) and measures an angle of 0...360.

When it is at 0, it outputs 0 V. When the shaft is rotated 90 clockwise, it gives a value of 90/360 * 10 V = 2.5 V. This value remains constant as long as the encoder shaft is not moved. The figure in example 1 shows the signal curve of such an absolute encoder.

The term "Full Scale" is often used with the abbreviation "F.S." to refer to the entire signal output scale. In the example above, F.S. = 10 V. Without knowing the maximum voltage, programming can also be done using percentage values. For example, 0 corresponds to 0% F.S. (0% of the maximum value, i.e. 0 V) and 360 corresponds to 100% F.S. (100% of the maximum value, i.e. 10 V). In this way, a signal output function can be accurately described without the use of a graph:

The figure shows the signal curve for these requirements in example 2. The output signals of absolute encoders can also be output via other interfaces, e.g. as output current or by pulse width modulation (PWM).

The Hall effect is a phenomenon in which an electrical voltage is generated in a current-carrying conductor (Hall element) when it is in an external magnetic field.

The effect is shown in the diagram opposite and can be explained as follows: When current flows through an electrical conductor, charge carriers (electrons) move through the conductor. If an additional magnetic field is applied, e.g. by an external magnet, the charge carriers are deflected perpendicular to the direction of the current. This is called the Lorentz force: It deflects charge carriers when they move and when an external magnetic field is applied. The electrons now accumulate at the edges of the conductor. The charge separation creates an additional voltage perpendicular to the direction of the current, called the Hall voltage.

If the external magnetic field changes as the magnet moves, the Hall voltage also changes - making it relatively easy to implement sensors. For example, if a circular, diametrically magnetized (north pole/south pole) permanent magnet is placed over a Hall element and the magnet is rotated, a sinusoidal output voltage curve can be measured. If the position of the magnet does not change, the measured value remains constant. However, a Hall sensor can only work if a current is flowing, otherwise the Lorentz force will not work. Therefore, Hall sensors require current during operation, even if the measurement position does not change.

In principle, external magnetic fields can interfere with Hall technology if no precautions are taken. Today, so-called gradient-based Hall sensors are used, which are largely insensitive to such interference.

The principle of this particular variant is that two or more Hall sensors are placed close to each other. The measuring magnet, which is very close to these two sensors, creates a difference in the signals of the two sensors because the curvature of the field is relatively strong. However, an external interfering field, which usually has a slight curvature, is 'seen' by both sensors in the same way. If only the difference between the two sensors (the gradient) is evaluated, then virtually only the measurement magnet is perceived and the measurement system is therefore very robust to external interference fields.

Most Hall encoders are digital encoders and process measurement signals with a certain resolution. The information is processed with an accuracy corresponding to the number of bits. The higher this value is, the finer the signals can be processed. Analogue output curves from digital devices therefore always have a fine gradation, the height of which is determined by the resolution. Typical resolutions are 10 bits, 12 bits or 14 bits, depending on the encoder model. For example, the angular resolution is 0.088 for 12 bits and 0.022 for 14 bits. The following simple observation helps to determine these values:

Since many Hall encoders are equipped with digital integrated circuits (ICs) that always send their signals with a certain delay, the update rate in milliseconds must be taken into account in the application. The update rate is the time between the acquisition of the measured value and the output of the signal in the angle encoder. It is usually between 96 s and 600 s for magnetic encoders with digital signal processing, but can be up to 3 ms for some multiturn encoders.

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