LINC-8 is the name of a minicomputer manufactured by Digital Equipment Corporation between 1966 and 1969. It combines a LINC computer with a PDP-8 in one cabinet, thus being able to run programs written for either of the two architectures.
79-614: The LINC-8 contains one PDP-8 CPU and one LINC CPU, partially emulated by the PDP-8. At any one time, the computer is in either 'LINC mode' or 'PDP-8 mode' - both processors can not run in parallel. Instructions are provided to switch between modes. In the LINC-8, all interrupts are handled by the PDP-8 CPU, and programs that rely on the interrupt architecture of the LINC can not be run. The LINC
158-474: A Teletype Model 33 ASR. Actually, the CRT is a specially modified unit based on a standard Tektronix oscilloscope modified to only be driven by D-A converters and an intensifier interface; there are no sweep circuits as found in conventional oscilloscopes. Most of the modifications involve custom highly stripped down plug in modules, which also house the actual knobs hooked to the lowest A-D channels. Arguably, this
237-401: A form factor that allows compactly installing many relays in a control panel. Although such relays once were the backbone of automation in such industries as automobile assembly, the programmable logic controller (PLC) mostly displaced the machine tool relay from sequential control applications. A relay allows circuits to be switched by electrical equipment: for example, a timer circuit with
316-478: A thermocouple or resistance thermometer sensor embedded in the winding. A polarized relay places the armature between the poles of a permanent magnet to increase sensitivity. Polarized relays were used in middle 20th Century telephone exchanges to detect faint pulses and correct telegraphic distortion . A reed relay is a reed switch enclosed in a solenoid. The switch has a set of contacts inside an evacuated or inert gas -filled glass tube that protects
395-470: A voltage spike dangerous to semiconductor circuit components. Such diodes were not widely used before the application of transistors as relay drivers, but soon became ubiquitous as early germanium transistors were easily destroyed by this surge. Some automotive relays include a diode inside the relay case. Resistors, while more durable than diodes, are less efficient at eliminating voltage spikes generated by relays and therefore not as commonly used. If
474-440: A LINC-8. In some cases, this means that they cannot be run on any other machine; in other cases, the LINC-8 merely represented a normal variation of drivers off of an otherwise non-descript PDP-8 system. An advantage of a PDP-8-based system is that PROGOFOP is superfluous here. If needed, the PDP-8 system can load PROGOFOP as well as a user program primarily LINC-oriented to get at the laboratory peripherals. The LINC convention of
553-489: A convenient means of generating fast rise time pulses, however although the rise time may be picoseconds, the exact timing of the event is, like all other types of relay, subject to considerable jitter, possibly milliseconds, due to mechanical variations. The same coalescence process causes another effect, which is a nuisance in some applications. The contact resistance is not stable immediately after contact closure, and drifts, mostly downwards, for several seconds after closure,
632-411: A feedback loop or sequential circuit . Such an electrically latching relay requires continuous power to maintain state, unlike magnetically latching relays or mechanically ratcheting relays. While (self-)holding circuits are often realized with relays they can also be implemented by other means. In computer memories, latching relays and other relays were replaced by delay-line memory , which in turn
711-425: A few minor LINC processor modifications to address the memory beyond the basic 4K total. Once this is accomplished, 4K memory "wings" can be added in a daisy-chained buss arrangement, which in theory could be expanded out as many as seven times to implement the entire 32K. As a practical matter, it is always difficult to implement on the "regular" PDP-8, and, in the case of the LINC-8, it becomes necessary to slow down
790-405: A fixed contact. If the set of contacts was closed when the relay was de-energized, then the movement opens the contacts and breaks the connection, and vice versa if the contacts were open. When the current to the coil is switched off, the armature is returned by a force, approximately half as strong as the magnetic force, to its relaxed position. Usually this force is provided by a spring, but gravity
869-437: A good conductor. Contactors with overload protection devices are often used to start motors. A force-guided contacts relay has relay contacts that are mechanically linked together, so that when the relay coil is energized or de-energized, all of the linked contacts move together. If one set of contacts in the relay becomes immobilized, no other contact of the same relay will be able to move. The function of force-guided contacts
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#1732776691923948-453: A laboratory environment, and the tapes can be carelessly pocketed, dropped, or even pierced and cut without losing the data stored on them. In 1969, DEC improved upon the LINC-8 with the PDP-12 , a similar combination computer for lab use, and the LINC-8 was cancelled. Few LINC-8 computers were ever built, numbering only in the low hundreds, and so the model is a rare sight today. As of 2008,
1027-404: A non-0 base number). This mathematical operation is primarily of interest in computer science , where it has varying effects depending on how a specific computer represents numbers. A ones' complement system or ones' complement arithmetic is a system in which negative numbers are represented by the inverse of the binary representations of their corresponding positive numbers. In such a system,
1106-442: A number is negated (converted from positive to negative or vice versa) by computing its ones' complement. An N-bit ones' complement numeral system can only represent integers in the range −(2 −1) to 2 −1 while two's complement can express −2 to 2 −1. It is one of three common representations for negative integers in binary computers , along with two's complement and sign-magnitude . The ones' complement binary numeral system
1185-608: A project to emulate the LINC-8 on modern hardware is underway within the Update computer society at Uppsala University . Ones%27 complement The ones' complement of a binary number is the value obtained by inverting (flipping) all the bits in the binary representation of the number. The name "ones' complement" refers to the fact that such an inverted value, if added to the original, would always produce an "all ones" number (the term " complement " refers to such pairs of mutually additive inverse numbers, here in respect to
1264-458: A relay could switch power at a preset time. For many years relays were the standard method of controlling industrial electronic systems. A number of relays could be used together to carry out complex functions ( relay logic ). The principle of relay logic is based on relays which energize and de-energize associated contacts. Relay logic is the predecessor of ladder logic , which is commonly used in programmable logic controllers . A mercury relay
1343-574: A relay uses an electromagnet to close or open the contacts, but relays using other operating principles have also been invented, such as in solid-state relays which use semiconductor properties for control without relying on moving parts . Relays with calibrated operating characteristics and sometimes multiple operating coils are used to protect electrical circuits from overload or faults; in modern electric power systems these functions are performed by digital instruments still called protective relays or safety relays . Latching relays require only
1422-447: A relay with several normally closed (NC) contacts may stick to the unenergized position, so that when energized, the circuit through one set of contacts is broken, with a marginal gap, while the other remains closed. By introducing both NO and NC contacts, or more commonly, changeover contacts, on the same relay, it then becomes possible to guarantee that if any NC contact is closed, all NO contacts are open, and conversely, if any NO contact
1501-475: A single pulse of control power to operate the switch persistently. Another pulse applied to a second set of control terminals, or a pulse with opposite polarity, resets the switch, while repeated pulses of the same kind have no effects. Magnetic latching relays are useful in applications when interrupted power should not affect the circuits that the relay is controlling. Electrical relays got their start in application to telegraphs . American scientist Joseph Henry
1580-404: A thin, self-renewing film of liquid mercury. For higher-power relays switching many amperes, such as motor circuit contactors, contacts are made with a mixtures of silver and cadmium oxide, providing low contact resistance and high resistance to the heat of arcing. Contacts used in circuits carrying scores or hundreds of amperes may include additional structures for heat dissipation and management of
1659-418: A typical EN 50005-compliant SPDT relay's terminals would be numbered 11, 12, 14, A1 and A2 for the C, NC, NO, and coil connections, respectively. DIN 72552 defines contact numbers in relays for automotive use: Where radio transmitters and receivers share one antenna, often a coaxial relay is used as a TR (transmit-receive) relay, which switches the antenna from the receiver to the transmitter. This protects
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#17327766919231738-416: Is a 12-bit ones' complement accumulator machine , whereas the PDP-8, while also a 12-bit accumulator machine, operates in two's complement arithmetic. Memory addressing on the two architectures is also different. On the LINC, the full address space is divided into 1024-word segments , two of which are selected for use at any one time: the instruction field and the data field . Direct access of data in
1817-435: Is a relay that uses mercury as the switching element. They are used where contact erosion would be a problem for conventional relay contacts. Owing to environmental considerations about significant amount of mercury used and modern alternatives, they are now comparatively uncommon. A mercury-wetted reed relay is a form of reed relay that employs a mercury switch , in which the contacts are wetted with mercury . Mercury reduces
1896-444: Is also trivial. The result can be only one of two cases. In case 1, operand 1 is −0 so the result is produced simply by subtracting 1 from 1 at every bit position. In case 2, the subtraction will generate a value that is 1 larger than operand 1 and an end-around borrow . Completing the borrow generates the same value as operand 1. The next example shows what happens when both operands are plus or minus zero: This example shows that of
1975-457: Is also used commonly in industrial motor starters. Most relays are manufactured to operate quickly. In a low-voltage application this reduces noise; in a high voltage or current application it reduces arcing . When the coil is energized with direct current , a flyback diode or snubber resistor is often placed across the coil to dissipate the energy from the collapsing magnetic field ( back EMF ) at deactivation, which would otherwise generate
2054-410: Is always recommended that PROGOFOP be loaded when attempting to use "complete" LINC programs on this system. Many operating systems were written for this machine; some were essentially slightly modified versions designed for the original LINC CPU it is partially based on. Bootup conventions allow an image of a custom version of PROGOFOP to first be loaded, followed by executing tape instructions to load
2133-406: Is because the PDP-8 program usually known as PROGOFOP is loaded there to handle all interrupts, traps, etc. It is possible to write a program for a "partial" LINC CPU, meaning using only the hardware that actually exists. Whenever an operation is performed that it cannot handle, the PDP-8 operation resumes. However, the LINC operation could have been terminated for a variety of reasons. As such, it
2212-562: Is characterized by the bit complement of any integer value being the arithmetic negative of the value. That is, inverting all of the bits of a number (the logical complement) produces the same result as subtracting the value from 0. Many early computers, including the UNIVAC 1101 , CDC 160 , CDC 6600 , the LINC , the PDP-1 , and the UNIVAC 1107 , used ones' complement arithmetic. Successors of
2291-427: Is characterized by the sign (high-order) bit being off (0) and all other bits being on (1). The lowest negative value is characterized by the sign bit being 1, and all other bits being 0. The table below shows all possible values in a four-bit system, from −7 to +7. Adding two values is straightforward. Simply align the values on the least significant bit and add, propagating any carry to the bit one position left. If
2370-630: Is closed, all NC contacts are open. It is not possible to reliably ensure that any particular contact is closed, except by potentially intrusive and safety-degrading sensing of its circuit conditions, however in safety systems it is usually the NO state that is most important, and as explained above, this is reliably verifiable by detecting the closure of a contact of opposite sense. Force-guided contact relays are made with different main contact sets, either NO, NC or changeover, and one or more auxiliary contact sets, often of reduced current or voltage rating, used for
2449-409: Is easily produced in a ones' complement adder. Simply add the positive and negative of the same magnitude. Although the math always produces the correct results, a side effect of negative zero is that software must test for negative zero. The generation of negative zero becomes a non-issue if addition is achieved with a complementing subtractor. The first operand is passed to the subtract unmodified,
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2528-412: Is held in place by a spring so that when the relay is de-energized there is an air gap in the magnetic circuit. In this condition, one of the two sets of contacts in the relay pictured is closed, and the other set is open. Other relays may have more or fewer sets of contacts depending on their function. The relay in the picture also has a wire connecting the armature to the yoke. This ensures continuity of
2607-452: Is necessary to control a circuit by an independent low-power signal, or where several circuits must be controlled by one signal. Relays were first used in long-distance telegraph circuits as signal repeaters: they refresh the signal coming in from one circuit by transmitting it on another circuit. Relays were used extensively in telephone exchanges and early computers to perform logical operations. The traditional electromechanical form of
2686-534: Is needed. A stepping relay is a specialized kind of multi-way latching relay designed for early automatic telephone exchanges . An earth-leakage circuit breaker includes a specialized latching relay. Very early computers often stored bits in a magnetically latching relay, such as ferreed or the later remreed in the 1ESS switch . Some early computers used ordinary relays as a kind of latch —they store bits in ordinary wire-spring relays or reed relays by feeding an output wire back as an input, resulting in
2765-442: Is often cited to have invented a relay in 1835 in order to improve his version of the electrical telegraph , developed earlier in 1831. However, an official patent was not issued until 1840 to Samuel Morse for his telegraph, which is now called a relay. The mechanism described acted as a digital amplifier, repeating the telegraph signal, and thus allowing signals to be propagated as far as desired. The word relay appears in
2844-407: Is partly offset by the increased costs in the external circuit. In another type, a ratchet relay has a ratchet mechanism that holds the contacts closed after the coil is momentarily energized. A second impulse, in the same or a separate coil, releases the contacts. This type may be found in certain cars, for headlamp dipping and other functions where alternating operation on each switch actuation
2923-400: Is present; changing the orientation of the reeds or degaussing the switch with respect to the solenoid's magnetic field can resolve this problem. Sealed contacts with mercury-wetted contacts have longer operating lives and less contact chatter than any other kind of relay. Safety relays are devices which generally implement protection functions. In the event of a hazard, the task of such
3002-479: Is said to have "wrapped around", a condition called an " end-around borrow ". When this occurs, the bit must be subtracted from the right-most bit. This phenomenon does not occur in two's complement arithmetic. It is easy to demonstrate that the bit complement of a positive value is the negative magnitude of the positive value. The computation of 19 + 3 produces the same result as 19 − (−3). Add 3 to 19. Subtract −3 from 19. Negative zero
3081-431: Is the condition where all bits in a signed word are 1. This follows the ones' complement rules that a value is negative when the left-most bit is 1, and that a negative number is the bit complement of the number's magnitude. The value also behaves as zero when computing. Adding or subtracting negative zero to/from another value produces the original value. Adding negative zero: Subtracting negative zero: Negative zero
3160-455: Is the precursor to the modern mouse interface; some software utilized knob twirling in a manner that would later suggest the two-dimensional form of a mouse; these are knobs controlling only one parameter at a time, etc. Some of these peripherals are simulated and are actually peripherals of the PDP-8. Any unimplemented operation stops the LINC CPU and interrupts the PDP-8 processor to handle
3239-438: Is to enable the safety circuit to check the status of the relay. Force-guided contacts are also known as "positive-guided contacts", "captive contacts", "locked contacts", "mechanically linked contacts", or "safety relays". These safety relays have to follow design rules and manufacturing rules that are defined in one main machinery standard EN 50205 : Relays with forcibly guided (mechanically linked) contacts. These rules for
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3318-522: Is used to split the flux into two out-of-phase components which add together, increasing the minimum pull on the armature during the AC cycle. Typically this is done with a small copper "shading ring" crimped around a portion of the core that creates the delayed, out-of-phase component, which holds the contacts during the zero crossings of the control voltage. Contact materials for relays vary by application. Materials with low contact resistance may be oxidized by
3397-463: The current page , that being the page where the instruction itself was located, or page 0 , the 128 words of memory at addresses 0-127. Indirect addressing can be used to produce 12-bit addresses. If more than 4K memory is implemented, the indirect addressing is extended to include the Data Field, thus it is possible to access any location indirectly in 32K maximum. Again, hardware limitations of
3476-526: The CDC 6600 continued to use ones' complement arithmetic until the late 1980s, and the descendants of the UNIVAC 1107 (the UNIVAC 1100/2200 series ) still do, but the majority of modern computers use two's complement . Positive numbers are the same simple, binary system used by two's complement and sign-magnitude. Negative values are the bit complement of the corresponding positive value. The largest positive value
3555-490: The CPU slightly just to add on the first additional 4K. Thus, as a practical matter, LINC-8 memory segments are limited to segment 0-3, or perhaps 0-7 on the few 8K implementations. However, basic 4K machines cannot address beyond 0-3 while extended memory models can attempt to address segments 0-37 octal even if non-existent memory. By convention, the segment 0 area is not available for normal fully emulated LINC operations. This
3634-478: The LINC-8 make it hard to achieve a total size of more than 8K total. Also implemented is the Instruction Field, making it possible to load larger programs into the same addressing space the Data Field controls. Transfer of control can be either direct or indirect as required. The new address is determined by first setting the new Instruction Field value, and then executing a JMP or JMS instruction into
3713-463: The LINC-based operating system. In some cases, the bootup procedure is accomplished manually right on the LINC console switches; later systems self-start the system after loading PROGOFOP. Other operating systems are actually more generic and are designed to mostly ignore the LINC side of things. These are PDP-8-only systems, although perhaps custom configured for the vagaries of the specifics of
3792-551: The Relay and Switch Industry Association define 23 distinct electrical contact forms found in relays and switches. Of these, the following are commonly encountered: The S ( single ) or D ( double ) designator for the pole count may be replaced with a number, indicating multiple contacts connected to a single actuator . For example, 4PDT indicates a four-pole double-throw relay that has 12 switching terminals. EN 50005 are among applicable standards for relay terminal numbering;
3871-539: The air, or may tend to "stick" instead of cleanly parting when opening. Contact material may be optimized for low electrical resistance, high strength to withstand repeated operations, or high capacity to withstand the heat of an arc. Where very low resistance is required, or low thermally-induced voltages are desired, gold-plated contacts may be used, along with palladium and other non-oxidizing, semi-precious metals. Silver or silver-plated contacts are used for signal switching. Mercury-wetted relays make and break circuits using
3950-463: The arc produced when interrupting the circuit. Some relays have field-replaceable contacts, such as certain machine tool relays; these may be replaced when worn out, or changed between normally open and normally closed state, to allow for changes in the controlled circuit. Since relays are switches , the terminology applied to switches is also applied to relays; a relay switches one or more poles , each of whose contacts can be thrown by energizing
4029-405: The carry extends past the end of the word it is said to have "wrapped around", a condition called an " end-around carry ". When this occurs, the bit must be added back in at the right-most bit. This phenomenon does not occur in two's complement arithmetic. Subtraction is similar, except that borrows, rather than carries, are propagated to the left. If the borrow extends past the end of the word it
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#17327766919234108-458: The change perhaps being 0.5 ohm. Multi-voltage relays are devices designed to work for wide voltage ranges such as 24 to 240 VAC and VDC and wide frequency ranges such as 0 to 300 Hz. They are indicated for use in installations that do not have stable supply voltages. Electric motors need overcurrent protection to prevent damage from over-loading the motor, or to protect against short circuits in connecting cables or internal faults in
4187-452: The circuit between the moving contacts on the armature, and the circuit track on the printed circuit board (PCB) via the yoke , which is soldered to the PCB. When an electric current is passed through the coil it generates a magnetic field that activates the armature, and the consequent movement of the movable contact(s) either makes or breaks (depending upon construction) a connection with
4266-421: The coil. Normally open (NO) contacts connect the circuit when the relay is activated; the circuit is disconnected when the relay is inactive. Normally closed (NC) contacts disconnect the circuit when the relay is activated; the circuit is connected when the relay is inactive. All of the contact forms involve combinations of NO and NC connections. The National Association of Relay Manufacturers and its successor,
4345-405: The coil. The advantage is that one coil consumes power only for an instant while the relay is being switched, and the relay contacts retain this setting across a power outage. A latching relay allows remote control of building lighting without the hum that may be produced from a continuously (AC) energized coil. In one mechanism, two opposing coils with an over-center spring or permanent magnet hold
4424-424: The console panel of the "real" LINC, then uses the PDP-8 to simulate most of them. The LINC-8 was built as a laboratory computer. It is small enough to fit in a laboratory environment, provided modest computing power at a low price, and included hardware capabilities necessary to monitor and control experiments. The LINCtape magnetic tape drive, designed by Wesley A. Clark for the LINC, is suitable for handling in
4503-525: The contact resistance and mitigates the associated voltage drop. Surface contamination may result in poor conductivity for low-current signals. For high-speed applications, the mercury eliminates contact bounce, and provides virtually instantaneous circuit closure. Mercury wetted relays are position-sensitive and must be mounted according to the manufacturer's specifications. Because of the toxicity and expense of liquid mercury, these relays have increasingly fallen into disuse. The high speed of switching action of
4582-479: The contacts against atmospheric corrosion ; the contacts are made of magnetic material that makes them move under the influence of the field of the enclosing solenoid or an external magnet. Reed relays can switch faster than larger relays and require very little power from the control circuit. However, they have relatively low switching current and voltage ratings. Though rare, the reeds can become magnetized over time, which makes them stick "on", even when no current
4661-411: The contacts in position after the coil is de-energized. A pulse to one coil turns the relay on, and a pulse to the opposite coil turns the relay off. This type is widely used where control is from simple switches or single-ended outputs of a control system, and such relays are found in avionics and numerous industrial applications. Another latching type has a remanent core that retains the contacts in
4740-546: The contacts. To prevent short over current spikes from causing nuisance triggering the armature movement is damped with a dashpot . The thermal and magnetic overload detections are typically used together in a motor protection relay. Electronic overload protection relays measure motor current and can estimate motor winding temperature using a "thermal model" of the motor armature system that can be set to provide more accurate motor protection. Some motor protection relays include temperature detector inputs for direct measurement from
4819-460: The context of electromagnetic operations from 1860 onwards. A simple electromagnetic relay consists of a coil of wire wrapped around a soft iron core (a solenoid), an iron yoke which provides a low reluctance path for magnetic flux, a movable iron armature , and one or more sets of contacts (there are two contacts in the relay pictured). The armature is hinged to the yoke and mechanically linked to one or more sets of moving contacts. The armature
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#17327766919234898-402: The entire first 1K being unavailable reserved for PROGOFOP is exchanged for the far smaller PDP-8 convention of reserving only 07600-07777 or the last 128-word page of the first 4K of the machine. This corresponds to a small reserved area at the end of LINC segment 3 in exchange for much greater overall flexibility. The PDP-8 divides its memory into 128-word pages . An instruction can reference
4977-545: The four possible conditions when adding only ±0, an adder will produce −0 in three of them. A complementing subtractor will produce −0 only when the first operand is −0 and the second is 0. Relay A relay is an electrically operated switch . It consists of a set of input terminals for a single or multiple control signals, and a set of operating contact terminals. The switch may have any number of contacts in multiple contact forms , such as make contacts, break contacts, or combinations thereof. Relays are used where it
5056-472: The instruction field is possible using 10-bit addresses. The data field can only be indirectly addressed. The Instruction field and Data field are theoretically capable of being chosen from up to 32 areas of 1K 12-bit words each as the maximum architecture is 32K total words. As a practical matter, few LINC-8 systems ever were expanded to 8K total. Memory expansion is accomplished first by adding PDP-8 memory extension hardware and extended memory instructions and
5135-410: The left switch register while the right switch register may have to also be set in the case of double word instructions such as most of the tape class. Booting certain operating systems consists of executing a tape read instruction directly from both sets of switches pressing the simulated DO key followed by pressing the simulated START 20 switch. In essence, the LINC-8 implements all of the functions of
5214-407: The mercury-wetted relay is a notable advantage. The mercury globules on each contact coalesce , and the current rise time through the contacts is generally considered to be a few picoseconds. However, in a practical circuit it may be limited by the inductance of the contacts and wiring. It was quite common, before restrictions on the use of mercury, to use a mercury-wetted relay in the laboratory as
5293-456: The monitoring system. Contacts may be all NO, all NC, changeover, or a mixture of these, for the monitoring contacts, so that the safety system designer can select the correct configuration for the particular application. Safety relays are used as part of an engineered safety system. A latching relay, also called impulse , bistable , keep , or stay relay, or simply latch , maintains either contact position indefinitely without power applied to
5372-415: The motor windings. The overload sensing devices are a form of heat operated relay where a coil heats a bimetallic strip , or where a solder pot melts, to operate auxiliary contacts. These auxiliary contacts are in series with the motor's contactor coil, so they turn off the motor when it overheats. This thermal protection operates relatively slowly allowing the motor to draw higher starting currents before
5451-491: The new field's corresponding 12-bit address, thus effecting a 15-bit address overall. The computer includes a number of LINC peripherals, which are controlled by special LINC mode instructions. These devices include analog inputs in the forms of knobs and jacks, relays for control of external equipment, LINCtape drives (the predecessor of the DECtape ), an oscilloscope -like cathode ray tube under program control, as well as
5530-527: The operated position by the remanent magnetism in the core. This type requires a current pulse of opposite polarity to release the contacts. A variation uses a permanent magnet that produces part of the force required to close the contact; the coil supplies sufficient force to move the contact open or closed by aiding or opposing the field of the permanent magnet. A polarity controlled relay needs changeover switches or an H-bridge drive circuit to control it. The relay may be less expensive than other types, but this
5609-523: The original LINC. An interesting feature is the FETCH/EXEC stop, which is implemented in all hardware in the LINC and PDP-12. The hardware, when enabled, continuously monitors instruction execution until specific conditions are met. This will cause a PDP-8 interrupt stalling the LINC program. Simulated console operations can be used to examine memory or make other changes, such as pressing the simulated DO key. The DO key executes any one instruction on
5688-418: The protection relay will trip. Where the overload relay is exposed to the same ambient temperature as the motor, a useful though crude compensation for motor ambient temperature is provided. The other common overload protection system uses an electromagnet coil in series with the motor circuit that directly operates contacts. This is similar to a control relay but requires a rather high fault current to operate
5767-420: The receiver from the high power of the transmitter. Such relays are often used in transceivers which combine transmitter and receiver in one unit. The relay contacts are designed not to reflect any radio frequency power back toward the source, and to provide very high isolation between receiver and transmitter terminals. The characteristic impedance of the relay is matched to the transmission line impedance of
5846-462: The relay is driving a large, or especially a reactive load, there may be a similar problem of surge currents around the relay output contacts. In this case a snubber circuit (a capacitor and resistor in series) across the contacts may absorb the surge. Suitably rated capacitors and the associated resistor are sold as a single packaged component for this commonplace use. If the coil is designed to be energized with alternating current (AC), some method
5925-569: The safety design are the one defined in type B standards such as EN 13849-2 as Basic safety principles and Well-tried safety principles for machinery that applies to all machines. Force-guided contacts by themselves can not guarantee that all contacts are in the same state, however, they do guarantee, subject to no gross mechanical fault, that no contacts are in opposite states. Otherwise, a relay with several normally open (NO) contacts may stick when energized, with some contacts closed and others still slightly open, due to mechanical tolerances. Similarly,
6004-418: The second operand is complemented, and the subtraction generates the correct result, avoiding negative zero. The previous example added 22 and −22 and produced −0. "Corner cases" arise when one or both operands are zero and/or negative zero. Subtracting +0 is trivial (as shown above). If the second operand is negative zero it is inverted and the original value of the first operand is the result. Subtracting −0
6083-476: The specifics. Most notably, the LINCtape is actually a PDP-8 peripheral; the tape class of LINC instructions are trapped and interrupt the PDP-8 which then emulates how a real LINC or PDP-12 would carry out the specifics of the latest tape instruction. Pressing a variety of keys on the seemingly present LINC console all cause PDP-8 interrupts; PROGOFOP is designed to emulate the functions as they would appear on
6162-404: The system, for example, 50 ohms. A contactor is a heavy-duty relay with higher current ratings, used for switching electric motors and lighting loads. Continuous current ratings for common contactors range from 10 amps to several hundred amps. High-current contacts are made with alloys containing silver . The unavoidable arcing causes the contacts to oxidize; however, silver oxide is still
6241-407: Was replaced by a series of ever faster and ever smaller memory technologies. A machine tool relay is a type standardized for industrial control of machine tools , transfer machines, and other sequential control. They are characterized by a large number of contacts (sometimes extendable in the field) which are easily converted from normally open to normally closed status, easily replaceable coils, and
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