万无一失，低速，可变磁阻传感器-Fail-Safe, Low
abstract: technical brief describes construction of a variable-reluctance sensor for detecting low- or medium-speed events. a simple circuit is shown utilizing two channels of an esd-protected rs-485 transceiver to deliver differential output data capable of providing fail-safe signals indicating sensor or cable malfunction.
variable-reluctance (vr) sensors are preferred for industrial and automotive environments because they withstand mechanical vibration and high-temperature operation up to 300°c. in most applications, they sense a steel target that is part of a rotating assembly. because the unprocessed signal amplitude is proportional to target speed, a sensor whose signal-processing circuitry is designed for high speed will cease to function as rotation slows.
hall-effect sensors are preferred for lower speeds (several pulses per second), but they require that a magnet be attached to the rotating assembly, making them prone to failure when the magnet is broken or damaged. neither type (vr or hall-effect) offers fail-safe detection of the processed signal in the event of failure in the cable or sensor.
the circuit of figure 1 is a fail-safe vr sensor suitable for low- to medium-speed operation. comprising of l1, r1, and a quad rs-422/rs-485 receiver (ic1), it provides the complementary, independent output signals vout and acitive-low vout. table 1 lists the resulting fail-safe modes. supply voltage can be +10v, +12v, or the control system's +24v dc source.
figure 1. this circuit provides a fail-safe, low-to-medium-speed, variable-reluctance sensor.
table 1. fail-safe modes (two cycles of vout or active-low vout) (vout, active-low vout) mode
(1,0) then (0,1), or (0,1) then (1,0) normal mode, both pulses valid
(1,0) then (0,0), or (0,0) then (1,0) failure, valid vout pulse, active-low vout failure, cable failure, or partial sensor failure*
(0,1) then (0,0), or (0,0) then (0,1) failure, valid active-low vout pulse, vout failure, cable failure, or partial sensor failure*
always (1,1) short-circuited cables or failure in ic1
always (0,0) severed cables, failure in ic1, or failure in q1 and q2
*system remains functional in failure modes.
coil l1 consists of 2600 turns of #32 magnet wire wound on a 0.800 steel bar of 0.200 diameter, with 0.125 protruding from the sensor face. a magnet attached to the back of the steel bar supplies necessary magnetic flux. the rotating target then causes a change in reluctance, hence a change in the amount of magnetic flux conducted, and therefore a change in the current induced in l1. r1 converts the l1 current to a time-varying voltage. this time varying voltage is applied to the inputs of ic1, whose wide input-voltage range (±25v), narrow input threshold (±0.2), and low input hysteresis (45mv typical) enable the vr sensor to operate at low speeds.
the separate and complementary outputs are derived from separate esd-protected inputs. ic1 outputs y1 and y2 can source up to 10ma of current. they alternately switch the logic-rated n-channel mosfets q1 and q2, which in turn provide vout and active-low vout. an ldo voltage regulator (ic2) generates the +5vdc required by ic1. figure 2 illustrates low- and medium-speed operation for the sensor.
figure 2. these figure 1 waveforms, produced by two targets 180° apart, illustrate low- and medium-speed operation: 4.9hz at 2.4 revolutions/sec (a), and 752.4hz at 376.2 revolutions/sec (b). channel 1 is vout, channel 2 is acitve-low vout, and channel 3 is the voltage across r1.
for +5v-supply applications in which a microcontroller can be located close to the sensor, only l1, r1, and ic1 are required for a direct interface. for +3v applications, replace ic1 with a max3096 ic.
a similar version of this article appeared in the november 22, 2001 issue of edn magazine.
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variable-reluctance (vr) sensors are preferred for industrial and automotive environments because they withstand mechanical vibration and high-temperature operation up to 300°c. in most applications, they sense a steel target that is part of a rotating assembly. because the unprocessed signal amplitude is proportional to target speed, a sensor whose signal-processing circuitry is designed for high speed will cease to function as rotation slows.
hall-effect sensors are preferred for lower speeds (several pulses per second), but they require that a magnet be attached to the rotating assembly, making them prone to failure when the magnet is broken or damaged. neither type (vr or hall-effect) offers fail-safe detection of the processed signal in the event of failure in the cable or sensor.
the circuit of figure 1 is a fail-safe vr sensor suitable for low- to medium-speed operation. comprising of l1, r1, and a quad rs-422/rs-485 receiver (ic1), it provides the complementary, independent output signals vout and acitive-low vout. table 1 lists the resulting fail-safe modes. supply voltage can be +10v, +12v, or the control system's +24v dc source.
figure 1. this circuit provides a fail-safe, low-to-medium-speed, variable-reluctance sensor.
table 1. fail-safe modes (two cycles of vout or active-low vout) (vout, active-low vout) mode
(1,0) then (0,1), or (0,1) then (1,0) normal mode, both pulses valid
(1,0) then (0,0), or (0,0) then (1,0) failure, valid vout pulse, active-low vout failure, cable failure, or partial sensor failure*
(0,1) then (0,0), or (0,0) then (0,1) failure, valid active-low vout pulse, vout failure, cable failure, or partial sensor failure*
always (1,1) short-circuited cables or failure in ic1
always (0,0) severed cables, failure in ic1, or failure in q1 and q2
*system remains functional in failure modes.
coil l1 consists of 2600 turns of #32 magnet wire wound on a 0.800 steel bar of 0.200 diameter, with 0.125 protruding from the sensor face. a magnet attached to the back of the steel bar supplies necessary magnetic flux. the rotating target then causes a change in reluctance, hence a change in the amount of magnetic flux conducted, and therefore a change in the current induced in l1. r1 converts the l1 current to a time-varying voltage. this time varying voltage is applied to the inputs of ic1, whose wide input-voltage range (±25v), narrow input threshold (±0.2), and low input hysteresis (45mv typical) enable the vr sensor to operate at low speeds.
the separate and complementary outputs are derived from separate esd-protected inputs. ic1 outputs y1 and y2 can source up to 10ma of current. they alternately switch the logic-rated n-channel mosfets q1 and q2, which in turn provide vout and active-low vout. an ldo voltage regulator (ic2) generates the +5vdc required by ic1. figure 2 illustrates low- and medium-speed operation for the sensor.
figure 2. these figure 1 waveforms, produced by two targets 180° apart, illustrate low- and medium-speed operation: 4.9hz at 2.4 revolutions/sec (a), and 752.4hz at 376.2 revolutions/sec (b). channel 1 is vout, channel 2 is acitve-low vout, and channel 3 is the voltage across r1.
for +5v-supply applications in which a microcontroller can be located close to the sensor, only l1, r1, and ic1 are required for a direct interface. for +3v applications, replace ic1 with a max3096 ic.
a similar version of this article appeared in the november 22, 2001 issue of edn magazine.
MQTT 5协议中的基础更改（一）
Skyworks一季度业绩亮眼，营收达12.02亿美元
DASKeyboard4终极版评测 表现让人一试难忘
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[组图]选频放大器
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人工智能对于农业与工业的应用，及未来应解决的问题
浅析高校能耗及节能管理
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