Patent Application
20150086026
The present disclosure relates generally to portable two-way radio devices and more particularly to portable two-way radio devices that are operated in the presence of volatile gasses and are designed in a manner to prevent ignition of volatile gasses such that the portable two-way radio device is considered intrinsically safe.
A portable two-way radio device is a hand-held device that the user carries on the user's person, such as in a holster or other carrier, and the user can operate the portable two-way radio by, for example, manipulating buttons and knobs on the radio, or by using a remote accessory also worn by the user that is connected to the portable two-way radio device. Portable two-way radios are used in a wide variety of applications where instant or near-instant communication is desirable. Two-way communication systems, including portable two-way radio devices, are used by public safety, emergency, rescue, fire, and industrial organizations, among others. Generally, two-way communication is a half-duplex type of communication where the radio device is either receiving, transmitting, or in standby/monitoring mode when on. When a user “keys up” a two-way radio, the radio will typically check to make sure the channel is clear and then begin transmitting after giving an audible indication to the user indicating the radio is transmitting and the user can commence speaking. The radio continues to transmit as long as the user has the radio keyed. To key the radio the user can press a “push to talk” button on the radio, or a remote radio microphone accessory, if used.
In some situations, the user of a portable two-way radio device may carry the radio, knowingly or unknowingly, into places where there are volatile gasses in the surrounding air. Examples of such places including mining operations, industrial and chemical settings, accident scenes, and so on. Given that portable two-way radio devices are battery powered, and contain various components that store energy in addition to the battery (e.g. capacitors, inductors), the potential exists for a discharge event or localized heat generation that can cause ignition of surrounding volatile gasses. To address such conditions manufacturers have taken measures to design portable two-way radio devices that are classified as being intrinsically safe for use by personnel who could operate in such conditions. To be rated as intrinsically safe, among other limitations, a battery powered electronic device must be designed to limit energy storage in the circuit components in case a fault occurs that releases the energy stored in those components, and precautions must be taken to limit energy available at the battery terminals to prevent sufficiently energetic sparks in case an inadvertent shorting between the terminals occurs. Furthermore, power provided to the device or components in the device from the battery may need to be limited in order to prevent thermal heating of small components to avoid creating a heat source sufficient to cause ignition of volatile gasses, dust, or other such compounds in the surrounding atmosphere.
The typical storage components in a given electronic device are capacitors and inductors. Capacitors store energy in the form of electrical charge and inductors store energy in the form of a magnetic field resulting from current through the inductor. Most of these passive components are small in typical electronic devices, including two-way radios, and will not store sufficient energy to be of concern, even when summed together under the assumption of an extreme fault condition. However, power handling components can have capacitance or inductance values large enough to be of concern, and may need to be limited.
In portable two-way radio devices, audio volume is particularly important since the user must be able to hear communications under potentially noisy conditions. The need for audio volume sufficient for the user to hear received audio over ambient sounds necessitates the use of speakers to play received audio signals. Speakers suitable for portable two-way radio applications typically use an inductive speaker coil that is driven by the audio amplifier. In an intrinsically safe application, however, the inductance of the speaker coil has to be limited to prevent exceeding energy storage specifications as well as avoiding excessive temperatures. Limiting the speaker coil inductance, though, limits the audio volume that can be achieved.
Accordingly, there is a need for an apparatus for achieving a desired audio volume without exceeding specified energy storage and temperature limits in an audio circuit of a device designed for intrinsically safe applications.
The accompanying figures, where like reference numerals refer to identical or functionally similar elements throughout the separate views, together with the detailed description below, are incorporated in and form part of the specification, and serve to further illustrate embodiments of concepts that include the claimed invention, and explain various principles and advantages of those embodiments.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.
[Reserved for claim 1 in sentence form, pending inventor and in-house counsel feedback].
The portable two-way radio device 100 includes a transceiver 102. The transceiver 102 includes both a radio transmitter and a radio receiver that are coupled to an antenna 104 for transmitting and receiving radio signals. The transceiver 102, although it may contain a processor such as a digital signal processor, operates under control of a controller 106 that is responsible for the general operation of the portable two-way radio device 100. The controller 106 can be a microprocessor or microcontroller that executes instruction code designed to cause the portable two-way radio device 100 to operate according to a design specification. The instruction code can be instantiated in a memory 108 that can include random access memory (RAM). The memory 108 can represent an aggregation of memory types including RAM, read only memory (ROM), and other types of memory such as reprogrammable non-volatile memory such as flash memory. To enable operation of the portable two-way radio device 100, the controller 106 is further coupled to several user interface elements 110, which can include a graphical display 112, a keypad and other buttons and knobs 114, an accessory connector 116, and a push to talk (PTT) button 118. The graphical display 112 can present textual and graphical material for visual display to a user. The keypad, buttons, and knobs 114 allow a user to input information, including selections of menu elements presented on the graphical display 112, as well as well as to select operational settings such as, for example, channel selection, audio volume, and so on.
As the main purpose of the portable two-way radio device 100 is for voice communication, it also includes an audio section or circuit 120 that processes audio signals received by the transceiver 102, and plays the received audio signals over one or more speakers in a speaker assembly 122. The audio section 120 can receive audio signals in acoustic form, from the user, via a microphone 134 which converts incident acoustic signals into electrical signals, as is known. Since the portable two-way radio device 100 is designed to be intrinsically safe, the inductance of any speaker coil must be small enough to avoid storing sufficient energy to cause a spark ignition if a fault occurred at peak current. Furthermore, intrinsically safe standards require a safety factor to ensure that even under extreme fault conditions the energy storage of a component will be limited to a safe level. Accordingly, the inductance value that is allowed under intrinsically safe standards is significantly smaller than the theoretical limit. The intrinsic safety limitation on the maximum inductance value limits the power that can be provided to a speaker coil, thus limiting the audio power and therefore the audio volume (e.g. sound pressure level). Given that it can be critical to hear voice communications, and that a user may be located in a noisy environment, it is desirable to provide a particular level of audio volume that may not be achievable using a conventional speaker with a speaker coil limited to the maximum allowable inductance under intrinsically safe standards.
To overcome the limitation resulting from inductance limits the speaker assembly 122 includes multiple speaker coils 128, 130, which are each driven by a separate audio power amplifier 124, 126, respectively. The total number of windings for the plurality of speaker coils 128, 130 can be substantially equal to that of a conventional speaker that produces the desired sound pressure level, but does not need to conform to intrinsically safe standards because the total inductance of a conventional speaker coil allows energy storage in excess of that allowed by intrinsically safe standards. The speaker coils 128, 130 can be disposed in a single speaker, or the speaker assembly 122 can include multiple speakers, each having one (or more) speaker coils, with each speaker coil being coupled to the output of a different audio power amplifier. The audio power amplifiers are individually current limited by redundant current limiters in a current limit block 132 which limit the current that can be drawn from a battery source 136. Each audio power amplifier 124, 126 draws current through a pair of series-connected redundant current limiters in the current limit block 132 that have fast response so that they limit current to the limited value even in the event of a fault (e.g. “short circuit,” or an interruption or open circuit) at the output of either of the amplifiers 124, 126. That is, the response time of the current limiters is such that the current through them cannot reach a spark ignition energy level. The current limit value can be set to a thermal ignition limit based on the direct current (DC) resistance of the speaker coil. That thermal ignition limit, with appropriate safety margin, can determine the inductance value of the speaker coil in view of an energy storage limit for spark ignition.
In order to prevent excessive current from reaching the speaker coils 210, 212, the audio power amplifiers 202, 204 are each supplied from the battery (+Vbatt) through a pair of series-connected current limiting circuits 218, 220, respectively. Thus, there are two current limiting circuits 218, 220 between each audio power amplifier 202, 204 and the battery. The current limiting circuits 218, 220 can be active current limiters that act quickly in the event of a fault, where the response time is on the order of microseconds. The current limiters can completely shut off current in response to an excessive load, such as a fault or short circuit in the audio power amplifiers 202, 204 or at the outputs 206, 208 of the audio power amplifiers 202, 204. Each of the redundant current limiters 218, 220 is set to a current limit at a level based on the DC resistance of the speaker coils 210, 212 and the maximum battery voltage (+Vbatt) for thermal ignition consideration.
Each of the audio power amplifiers 202, 204 receive the same input signal that is provided to a common input 226. The signal provided to the common input 226 can be provided by a receiver, such as a receiver in a transceiver 102 of
Accordingly, the arrangements and audio circuits exemplified herein provide the benefit of increasing the audio volume capable of being generated by a speaker under intrinsically safe design limitations by providing a second speaker coil that is likewise subject to the same intrinsically safe design limitations. Additional speaker coils can be added to meet desired acoustic sound pressure levels. Each speaker coil is driven with a substantially identical signal from a separate audio power amplifier. The benefit is particularly useful for intrinsically safe portable two-way radio devices where it is necessary to meet audio volume levels that allow users to hear voice communication clearly over ambient noise, which may be significant. Using a single speaker coil that meets intrinsically safe standards may not produce a sufficient audio volume for a portable two-way radio device. In fact, the total number of windings between the multiple speaker coils used in the various embodiments may be equivalent to a standard number of windings for a given speaker. By separating the total number of windings into separate coils, each driven by a dedicated separate audio power amplifier that is redundantly current limited, substantially the same audio performance can be achieved under intrinsically safe design limitations as using one coil with an equivalent number of windings where meeting intrinsically safe standards is not necessary.
In the foregoing specification, specific embodiments have been described. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the invention as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of present teachings.
The benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential features or elements of any or all the claims. The invention is defined solely by the appended claims including any amendments made during the pendency of this application and all equivalents of those claims as issued.
Moreover in this document, relational terms such as first and second, top and bottom, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms “comprises,” “comprising,” “has”, “having,” “includes”, “including,” “contains”, “containing” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises, has, includes, contains a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by “comprises . . . a”, “has . . . a”, “includes . . . a”, “contains . . . a” does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises, has, includes, contains the element. The terms “a” and “an” are defined as one or more unless explicitly stated otherwise herein. The terms “substantially”, “essentially”, “approximately”, “about” or any other version thereof, are defined as being close to as understood by one of ordinary skill in the art, and in one non-limiting embodiment the term is defined to be within 10%, in another embodiment within 5%, in another embodiment within 1% and in another embodiment within 0.5%. The term “coupled” as used herein is defined as connected, although not necessarily directly and not necessarily mechanically. A device or structure that is “configured” in a certain way is configured in at least that way, but may also be configured in ways that are not listed.
It will be appreciated that some embodiments may be comprised of one or more generic or specialized processors (or “processing devices”) such as microprocessors, digital signal processors, customized processors and field programmable gate arrays (FPGAs) and unique stored program instructions (including both software and firmware) that control the one or more processors to implement, in conjunction with certain non-processor circuits, some, most, or all of the functions of the method and/or apparatus described herein. Alternatively, some or all functions could be implemented by a state machine that has no stored program instructions, or in one or more application specific integrated circuits (ASICs), in which each function or some combinations of certain of the functions are implemented as custom logic. Of course, a combination of the two approaches could be used.
The Abstract of the Disclosure is provided to allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In addition, in the foregoing Detailed Description, it can be seen that various features are grouped together in various embodiments for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed embodiment. Thus the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separately claimed subject matter.
