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MINIATURE SIGNAL RELAY

FUNCTIONS AND NOTES ON CORRECT USE

MINIATURE SIGNAL RELAY
FUNCTIONS AND NOTES ON CORRECT USE
Document No. ER0144EJ3V0UM00 (3rd edition) Date Published December 2000 P CP(K)
Printed in Japan
CONTENTS
3.1 General Classification ............................................................... 3.2 Operational Functions .............................................................. 7 7
3.3 Contact Arrangement ............................................................... 10 3.4 Contact Material .................................................................... 12
4. NOTES ON CORRECT USE ...................................................... 13
4.1 General ........................................................................... 13 4.2 Connecting Contact Load (Minimum Load, Contact Protection Circuit) ............................................ 13 4.3 Driving Relays (Ambient Temperature, Maximum Applied Voltage, Hot Start, Latching Relay, Drive Waveform, Non-operation and Holding Voltages) .................................................. 18 4.4 Environments (Ambient Temperature, Humidity, Atmosphere, Atmospheric Pressure, Vibration and Shock, Influence of Magnetic Fields) ......................................................... 23 4.5 Influence of Relay Operation on Surroundings (Electromagnetic Noise, Arc Discharge, Generation of Leakage Magnetic Flux) ............. 25 4.6 Mounting (Design of Printed Circuit Boards, Relay Mounting Position, Mounting) .................... 25 4.7 Cleaning (Cleaning Solvent, Avoid Ultrasonic Cleaning) .......................................... 27 4.8 Handling Relays (Use of Magazine Case Stoppers, Dropped Relay) ....................................... 27 4.9 Using Surface Mount Relays (Mounting Pad, Glue Pads, Solder Reflow ) ............................................. 28
5. ELECTRICAL CHARACTERISTICS MEASUREMENT (Contact Resistance, Operate Voltage, Time Characteristics, Insulation Resistance, Breakdown Voltage) ............................................................ 30 6. TERMINOLOGY ............................................................... 33
6.1 Terms Related to Standards .......................................................... 33 6.2 Supplements ....................................................................... 36
1. INTRODUCTION
2. PRODUCT CODE LEGEND
NEC offers small, new, and ultra small type miniature signal relays. The product names of these relays consist of codes indicating the function of each relay. EA2-3 S N U Option Latch type: None: Non-latch ty pe S: Single-coil latch type T: Double-coil latch type Nominal coil voltage: Value of nominal coil voltage Series name
Electromechanical relay Miniature relay Miniature signal relay Miniature power relay Sealed contact relay Reed relay Mercury reed relay Solid-state relay
Figure 1 Classification of Relays 3.2 Operational Functions This section describes the operations of the coil, which is the input section of a relay, and the contacts, which constitute the output section. Generally, when a current flows through the coil of a relay, the contacts operate. The contacts of an ordinary relay release when a current ceases to flow through the coil. With some relays, however, contacts, once they have operated, remain "set" and do not return to the original state even after the current supplied to the coil is removed. These relays are called latching relays. (Incidentally, the former type of relay is called a non-latch type or current holding type.) The latching relay is further divided into two types by classification of coil: single coil latch type which has only one coil, and double coil latch type, which has two coils. (1) Relay operation Figures. 2.1 through 2.3 illustrate the operations of the three types of relays mentioned above by using timing charts.
1 Non-latch type (current holding type)
Energized Coil Not energized
Operate Contacts Release
Figure 2.1 Timing Chart of Non-Latch Type
2 Single coil latch type
Energized + Coil 0 - Set Contacts Reset Not energized Energized
Figure 2.2 Timing Chart of Single Coil Latch Type
3 Double coil latch type
+ 0 + 0 Not energized Energized Not energized
Set Coil Reset Coil
Energized
Set Contacts Reset
1 Non-latch type
Figure 3.1 (a) shows the state where no current flows through the coil. When voltage is applied to the pole shown in Figure 3.1 (b), the contacts operate.
(a) Not energized
(b) Energized Figure 3.1 Non-Latch Type Operation
2 Single coil latch type
When voltage of the polarity specified to set (S in figure 3.2 (a)) the coil is applied to the coil (in figure 3.2 (b)), the contacts operate. Even after the coil is deenergized, the contacts remain in the operate state (figure 3.2 (c)). When voltage of the polarity specified to reset (R) the coil is applied to the coil, the contacts release (figure 3.2 (d)).
(a) Not energized (reset state)
(b) After voltage application (set state)
R Return to (a)
(c) Not energized (set state)
(d) After voltage application (reset state)
Figure 3.2 Single Coil Latch Type Operations
3 Double coil latch type
As shown in figure 3.3 (a) through (d), the double coil latch type relay has two separate coils each of which operates (sets) and releases (resets) the contacts.
(a) Not energized (reset state)
(b) After voltage applied to set coil (set state)
Returns to (a)
(c) Not energized (set state)
(d) After voltage applied to reset coil (reset state)
Figure 3.3 Double Coil Latch Type Operations
Break contact Transfer contacts Common contact Before operation Common contact During operation Common contact After operation Make contact Break contact Make contact Break contact Make contact
Break contact Continuous contacts
Make contact
Break contact
Make contact
Break contact
Make contact
Common contact Before operation
Common contact During operation
Common contact After operation
Figure 4 Operation States of Each Contact (1) Functions of transfer contacts The common contact of the transfer contacts touches the make contact after it has been separated from the break contact when the relay operates. When the relay releases, the common contact is separated from the make contact and comes in contact with the break contact. Therefore, when the relay operates, there is a time during which the common contact is not in contact with either make or break contacts (transfer time). For this reason, the transfer contacts may also be referred to as "break-before-make" (BBM) contacts. These operations are illustrated in the timing chart below.
Energized Coil voltage Not energized
Break contact ON OFF
Make contact ON
OFF Operate time Bounce time Transfer time Transfer time Release time Bounce time
Figure 5.1 Timing Chart of Transfer Contacts
1 The operate time is the time during which the make contact comes in contact with the common contact (ON
2 An electromechanical relay such as a miniature signal relay has a bounce time until the contacts are
3 Similarly, when the relay is released, and therefore, when the common contact is separated from the make
contact and comes in contact with the break contact, transfer time and bounce time exist. The values of these times are same as those when the relay operates. A relay of this contact arrangement is used to switch over between two circuits and to completely set one circuit free from the influences of the other circuit. (2) Functions of continuous contacts The common contact of the continuous contacts may come in contact with both the make and break contacts (continuous time). This is illustrated by the timing chart in figure 5.2.
Energized Coil voltage Not energized Break contact ON OFF Make contact ON OFF Bounce time Operate time Release time Bounce time
Continuous state
Continuous time
Figure 5.2 Timing Chart of Continuous Contacts As shown in this timing chart, the common contact comes in contact with the make contact before the break contact is opened. For this reason, the continuous contacts may also be referred to as "make-before-break (MBB) contacts".
A relay of this contact arrangement is used to continuously switch over from circuit A to B as shown in figure 6, where, when viewed from the power source, there is a little deenergized state and the two circuits are instantaneously connected in parallel.
1 Break contact 2 3 1 Before operation Make contact 2 During operation Circuit A Power source Circuit B 3 After operation
Figure 6 3.4 Contact Material
Example of Use of Continuous Contacts
Movable contact
Gold alloy overlay Base metal Base
Stationary contact
Normal type
Ultrasonic cleaning type
Figure 7 Cross-Sectional View of a Contact
4. NOTES ON CORRECT USE
4.1 General (1) Never allow the contact load to exceed the maximum ratings otherwise, the lifetime of the relay will be dramatically shortened. The lifetime specified in the catalog is for certain load conditions, and other factors must be taken into consideration in actual circuits. Therefore, an accurate lifetime must be measured in the actual circuit. The table below shows load current range guideline.
Current range 100 µA to 1mA GOOD · Contacts may be unstable. · Thermal electroApplication motive force and contact noise should be taken into consideration. 1mA to 0.5A VERY GOOD 0.5A to 2A NOT SO GOOD for some cases · Contacts are stable and highly reliable. · Infrequent operation poses no problem, but frequent operation deteriorates contact stability. · Use of a power relay is preferred for 1 A or higher.
(2) When using the relay with a high current or high capacitance load, an inrush current may cause contact dislocation or deposition therefore check the feasibility of use in the actual circuit. (3) Be sure to use the relay at an ambient temperature within the maximum ratings otherwise, the life of the relay will be radically shortened. If use outside the specified temperature range in unavoidable, consult NEC. (4) With a relay whose coil polarity is specified in its internal circuit diagram, apply the polarity of the rated voltage as specified. Note that when a rippled DC power source is used, abnormalities such as beat in the coil may occur. (5) Exercise care when handling the relay so as not to apply shock to it or drop it. (6) The flow soldering conditions are for 5 to 10 seconds at 250°C. (7) When cleaning, use alcohol, or a water-based solvent. Avoid using ultrasonic cleaning. If it is necessary to use ultrasonic cleaning, use a product resistant to such cleaning. (8) Sonic noise may occur during the relay operation. Depending on the mounting position, the sonic noise may sound intolerable, so be sure to check the mounting position thoroughly prior to use. 4.2 Connecting Contact Load (1) Minimum load Use the relay at a voltage and current higher than the minimum load otherwise, the contact resistance will increase and signal cannot be correctly transmitted. In addition, self-cleaning effect, which electrically and mechanically eliminates minute substances generated on the contact surface when the contacts are opened and closed, cannot be expected.
(2) Contact protection circuit By providing a protection circuit that suppresses transient current and voltage applied to the contacts when the contacts are opened or closed, the switching life of a relay can be improved. The applicable protection circuit differs depending on the load type of the contacts.
1 Protection circuit classified by load type
(a) Inductive load With an inductive load, when the contacts are opened to break the circuit, a counter electromotive force is generated. This voltage causes arc discharge between the contacts. The charged energy accelerates metal deposition and wear on the contact surface. A protection circuit is therefore used to absorb the counter electromotive force.
Contacts open
E Inductive load E
Figure 8 Inductive Load Circuit
Table 1 shows examples of protection circuits. Table 1 Inductive Load Contact Protection Circuit
Protection element Circuit example Remarks
Inductive load
contact voltage (V)
Capacitor + resistor (CR circuit)
Inductive load
Varistor
Inductive load
High voltage is suppressed by using the voltage characteristics of the varistor.
Diode Inductive load
Pay attention to the reverse breakdown voltage of the diode.
Diode + Zener diode Inductive load
The ON time of the diode is controlled by using the Zener voltage characteristic and the recovery time of the relay can be shortened.
(b) Capacitive load Never use a connection with a capacitor only as shown in table 2. Table 2 Examples of Wrong Circuits Using Capacitiors WRONG
This circuit is effective for arc suppression when the contacts are opened, but when the contacts are
WRONG
This circuit is effective for arc suppression when the contacts are opened, but when the contacts are closed a capacitor chargc Load
closed a capacitor shortLoad
circuit current flows, making the contacts more susceptible to metal deposition.
ing current flows, making the contacts more susceptible to metal deposition.
(c) Loads of lamps and the like (inrush current) Some loads, such as tungsten lamps, have a low initial resistance so that an inrush current of 10 times as high as the steady-state current may flow through the relay on power application. A high inrush current may also flow when the relay is used to switch loads such as motors, capacitors, and electromagnetic solenoids. In these cases, it is necessary to keep the current to within the maximum rated value. Therefore, a current-limiting resistor is connected to the contacts in series.
Without current-limiting resistor Current With current-limiting resistor Contacts Lamp 0 Power source Time
Figure 9 Inrush Current of Loads from Lamps and the Like
(d) Load with large stray capacitance If the wiring length of a circuit where a relay is used is long, an inrush current that is generated due to a stray capacitance poses a problem. As shown in figure 10, the electric energy charged to the line capacitance is discharged directly through the contacts when the contacts are closed (ON). Generally, the stray capacitance must be taken into consideration if the wiring length reaches several tens of meters. In this case, a current-limiting resistor or surge suppressor coil is connected in series to the contacts to suppress the peak current.
Surge suppressor coil
Contacts Power source
Wiring cable
Figure 10 Stray Capacitance
1 Generally, use the relay in the specified temperature range at less than the maximum ratings. Note, however,
that the maximum must operate voltage of the coil changes with temperature, and must be confirmed before the relay is used (refer to (2) in "Maximum applied voltage").
2 The operating characteristics of the relay change with ambient temperature (refer to figure 11 below). Confirm
the temperature condition in the application set where the relay is to be used. characteristics of a relay, refer to Technical Documents.
For the temperature
Must operate Must release
Operate Release
Ambient temperature Ta (°C)
Figure 12 Coil Voltage vs Temperature Derating Characteristics (Example)
Degree of distribution
Must release voltage
Must operate voltage
Must release voltage (rated)
Holding voltage
Non-must operate voltage
Must operate voltage (rated)
Rated voltage
Figure 13 Example of Distribution of Relay Operate Voltage (5) Drive waveform It is not desirable that the waveform of the voltage applied to a relay coil gradually increase and decrease. The voltage must instantaneously rise and fall as a pulse. If the voltage gradually increases and decreases, the relay does not perform its snap action, and its fullest performance cannot be attained.
Pulse
Correct
Incorrect (avoid) Non-pulse
Figure 14 Relay Drive Waveform
(6) Drive circuit (latching relay) The drive circuit of a latching relay is especially important. Therefore, special attention needs to be paid to the drive circuit of a latching relay in this section.
1 Since the coil of a relay has an inductive impedance, a counter electromotive force is generated when the
circuit is opened. This voltage may damage the relay driver IC. Therefore, with a double coil latch type current holding relay, a diode is connected in parallel with each coil, as shown in figure 13. With a single coil latching type relay, however, a diode cannot be used because the current direction of the coil is inverted. Therefore, the driver circuit of this relay must be designed and confirmed in the actual circuit.
Set coil +
Reset coil +
- Set pulse
Reset pulse
Figure 15 Drive Circuit of Latching Relay (Example)
2 A latching relay is driven by a pulsating coil voltage. The pulse width of this drive voltage must be 10 ms
or wider. If the pulse is too short, the relay may not operate.
3 Apply a voltage to the coil in the polarity specified by the internal connection diagram of the relay. With a
double coil latching type relay, do not apply voltage in a manner that both the set and reset coils are energized at the same time.
4 A latching relay is factory-set to the reset state for shipment. However, it may be set while being transported
due to vibration or shock. Make sure that the relay is reset when its application system starts operating. When the relay is employed in a portable system, the circuit must be designed so that the relay is reset at the beginning of the operation of the system because the relay may be set by unexpected vibration or shock.
5 Whe configuring a self-holding circuit that uses the self break contacts of the relay, note that the coil drive
circuit is disconnected by the self-contacts, causing problems such as self oscillation. (7) Connection of coil diode In the case of loads, such as solenoid and electromagnetic clutches, that produce large discharge energy when the contacts are opened, connect a Zener diode on the drive transistor side. Particularly, if the diode is connected to the coil in parallel, the counter electromotive force of the coil returns the current gradually when the relay is released, and thus may slow down the opening of the contacts, intensifying wear on the contacts. (8) Opening / closing frequency If the contacts are opened / closed frequently with a high current load, repeated electric discharges may cause contact metal deposition or damage to the contact spring.When using the relay with a high current load with frequent opening / closing of the contacts, consult NEC.
(9) Long continuous energizing of coil If the coil is energized continuously for a long time, the coil temperature may rise, promoting generation of organic gas inside the relay, which is likely to cause trouble in the contacts. When using a circuit requiring constant operation, consider the possibility of using a latching relay that does not need continuous energizing of the coil. (10) Instantaneous voltage drop of circuit When the same power source is used for the relay drive circuit and the load circuit in a circuit such as a lamp load circuit where an inrush current flows, the moment the contacts are closed the source voltage may drop if the power source capacitance is small. In this case, the relay may be released or an oscillation phenomenon where the relay repeatedly releases and operates may occur. Add power source capacitance or a smoothing circuit to prevent this phenomenon. (11) Malfunctioning due to unwanted voltage Because the miniature signal relay is designed to be highly sensitive, it may operate by mistake if a pulsating noise whose pulse width is shorter than the normal drive voltage is applied to the coil for a short time. Therefore, exercise care that such an unwanted voltage is not applied to the coil. The device recovers from this phenomenon after the coil voltage has been removed, and then contacts have operated, as shown in the timing chart in figure 16. The relationship between the magnitude of the coil voltage that causes the above phenomenon and the pulse width is similar to that illustrated below, however, this should be confirmed with the actual circuit. (Timing chart of unwanted voltage) (Relation between pulse time width and coil voltage)
Pulse time width (ms) 1.0 Coil voltage 0.5 Pulse time Contacts operate Recovery Operate Recovery 0
Figure 16 Malfunctioning due to Unwanted Voltage
(12) Momentary interception failure of continuous contacts The continuous contacts are suitable for applications where two circuits must be changed over in a time shorter than that of the transfer contacts because the continuous contacts are continuously switched. However, a interception failure does occur in the application circuit because of the bounce of the contacts, and a thorough evaluation must be made before the continuous contacts are actually used in an application. Because the miniature signal relay has little bounce, the momentary power failure is kept to a relatively short time. For details, consult NEC. (Momentary interception failure evaluation circuit)
B Power supply M Current measuring resistor B 2R M Contact current (operating status) Recovery 0 Energization R Coil voltage 0 Continuous Operate Continuous
(Timing chart of momentary interception failure)
Note If a momentary power failure occurs, the voltage across the resistor is zero. Figure 17 Momentary Power Failure of Continuous Contacts
Changes in must operate voltage
Set sample ON ON OFF OFF ON OFF
Number of samples : 10 each
Maximum value I Minimum value ON I II III IV V VI ON ON V II
ON III
OFF IV
OFF OFF OFF VI
Mounting method
Figure 18 Dense Mounting
4.5 Influence of Relay Operation on Surroundings (1) Electromagnetic noise Switching the relay coil generates a high electromotive force due to induction. In general, a surge suppression circuit is connected in parallel with the relay coil to suppress generation of this electromotive force. However, if this suppression circuit is not appropriate, electronic circuits such as microcontrollers may malfunction due to the surge generated. Add an appropriate absorption circuit to prevent electronic circuits from malfunctioning due to the surge generated. (2) Arc discharge Connecting / disconnecting a high current at the relay contacts generates an arc discharge. This discharge may cause electronic circuits such as microcontrollers to malfunction and therefore it is necessary to take appropriate measures. (3) Generation of leakage magnetic flux Leakage magnetic flux exists in the vicinity of the relay in the magnetized state. Mounting a magnetic sensor, etc. close to the relay may cause malfunctioning. 4.6 Mounting (1) Design of printed circuit boards
1 If an electronic circuit such as a microcontroller is placed close to a relay, noise generated by the relay may
cause malfunctioning.
2 When designing patterns keep to the shortest possible distance in wiring. 3 For the printed circuit board on which a relay is mounted, use a board o 1 mm or more in thickness. If the
printed circuit board is not thick enough, it may be subject to warpage which will add tension to the relay, causing variations in the relay characteristics. Because a flexible printed circuit borad is particularly thin, it is necessary to solder near the root of the relay pins. Since preliminary soldering of the pin root part is often insufficient, its solder is likely to become loose.
4 If a thermal cycle is applied to the soldered part, cracks may be generated in it. Special care is required
for the relay location, base material and through hole shape. (2) Relay mounting position The vibration resistance and shock resistance of a relay are greatly affected by its mounting position. It is particularly important to select the mounting position to prevent the break contacts from being instantaneously cut due to vibration and shock. The vibration resistance and shock resistance are at a minimum when the direction of vibration and shock applied to the relay matches the operation direction of the armature (mobile iron piece) and contacts. Therefore, if it is possible to anticipate the direction of vibration or shocks, mount the relay so that the direction in which vibration of shocks are applied is perpendicular to the direction of the relay armature operation figure 19 shows the direction of relay armature operation.
Figure 19 Direction of Armature Operation
(3) Notes on mounting
1 Chucking
When a relay is mounted using an automatic machine, note that application of an excessive external force to the cover at the time of chucking or insertion of the relay may damage or change the characteristics of the cover.
2 Temporary securing to printed circuit board
Avoid bending the pins to temporarily secure the relay to the printed circuit board. (Refer to figure 20.) Bending the pins may degrade sealability or adversely influence the internal mechanism. Pin bending may be allowed under certain conditions in the case of miniature signal relays. Contact NEC for details.
Good example Bad example
Figure 20 Bending Relay Pins
3 Soldering work
4 Pin cutting after soldering
Do not cut the pins of the relay with a revolving blade or an ultrasonic cutter, because vibration that is applied to the relay during the cutting may change the relay characteristics.
4.7 Cleaning (1) Cleaning solvent Use of alcohol or water-based cleaning solvents is recommended. Never use thinner or benzene because these solvents may damage the relay housing. A sealed type relay can be immerse-cleaned because solvent does not penetrate inside the relay. (2) Avoid ultrasonic cleaning. Ultrasonic cleaning may cause a break in the coil wire or sticking of the contacts due to the energy of vibration. Use ultrasonic cleaning with only the models designed for it. 4.8 Handling Relays (1) Use of magazine case stoppers Relays are packaged in magazine cases for shipment. When some relays are taken out from the case and space is freed inside the case, be sure to secure the relays in the case with a stopper. If the relays are not well secured, vibration during transportation may cause contact problems.
Stopper Stopper
Push in to secure the relays.
Figure 21 Storage in Magazine Case (2) Do not use relays that have been dropped. If an individual relay product falls from the work table, etc. a shock of 1000 G or more is applied to the relay and its functions may be destroyed. Even if the shock is apparently weak, confirm that there is no abnormality before using the relay.
4.9 Using Surface Mount Relays This section describes specific points to be noted when using a surface mount relay. For common points for both types, refer to the previous section. (1) Mounting pad Determine the dimensions of the mounting pads on a printed circuit board taking into consideration such factors as solderability, insulation, and mounting variations of the automatic mounter. Use the dimensions of the mounting pads set forth in the catalog of the relay for reference.
Figure 22 Dimensions of the Relay Mounting Pad (Example of EB2 Series)
(2) Solder reflow The surface mount relay is highly resistant to heat. However, solder the relay under the correct temperature conditions so that the full performances of the relay can be attained. IRS (infrared ray reflow soldering) and VPS (vapor phase soldering) methods are recommended. In addition, air reflow soldering may be also used. Whichever soldering method is used, be sure to confirm the temperature conditions for soldering and the influences of soldering on the relay in advance.
Tmax.: 235
Temperature (°C)
200 sec.
30 sec. 80 sec.
Tmax. : 215 Temperature (°C) 200°C max. 165°C max. 100°C max.
60 s max. 60 s 90 s max.
5. ELECTRICAL CHARACTERISTICS MEASUREMENT
This chapter describes some methods to measure the electrical characteristics of a relay. The methods introduced here are examples. To conduct acceptance tests, consult NEC. These measurement methods conform to JIS-C5442 (testing methods of small electromagnetic relays for control applications). (1) Contact resistance
1 The resistance between contacts when they are closed (ON) is measured by the voltage drop method.
Set the supply voltage (voltage between pins when the contacts are open) to 6 Vdc and the measurement current to 1 A with controlling current limit resistance decreasingly. As a simple method, use a low ohmmeter by Hewlette-Packard (HP-4338A).
2 To measure the resistance of the make contact, apply the rated voltage to the coil.
3 The contact resistance is the value including the conductor resistance of the pins.
Relay A Nominal coil voltage V 6 Vdc
Figure 24 Measuring Contact Resistance (2) Operation voltages (must operate and must release voltages)
1 Apply a pulsating voltage to the coil and observe the contact state. To generate the coil voltage, use of a
programmable power supply is convenient. To observe the contact state, apply the potential signal of the contacts to the input of the inverter and observe changes in the output state (voltage drop when the contacts are closed, and supply voltage when the contacts are open).
5V Programmable power supply I / O a Relay
Inverter
Contact potential signal
Personal computer (I / O port used)
Contact signal
Figure 25 Measuring Operation Voltages
2 To measure the must operation voltage, gradually increase the pulse voltage applied to the coil. To measure
the must release voltage, decrease the coil voltage stepwise from the rated voltage to a certain value.
3 If a pulsating voltage cannot be obtained easily, use a slope voltage. In this case, however, the measured
value will not be accurate.
Voltage Rating (Pulse) Must operate
Must release 0 Time
Voltage Rating Must operate (Slope) Must release
Figure 26 Measuring Waveform of Operation Voltage (Coil Voltage) (3) Time characteristics (operate time and release time)
1 Apply a pulse voltage to the coil and measure the time difference required for the contacts to change their
states.
2 A single pulse with a pulse width of 10 ms is the best as the coil voltage. However, a repetitive pulse at
about 10 Hz can also be used. To observe the contact state, connect a load of 5 V, 10 mA and use an oscilloscope.
3 The time characteristics of the non-latch type (current hold type) relay can be measured with the following
circuit. Apply voltage in both the positive and negative directions to the single coil latch type relay. With the double coil latch type, apply voltage to the set and reset coils alternately.
Load resistance
Pulse generator, etc.
Load voltage
Oscilloscope
Figure 27 Measuring Time Characteristics
(4) Insulation resistance
1 Measure the electric resistance between insulated conductors with a megohmmeter.
2 Measure the insulation resistance at the following relay pins:
(a) Between opposing contacts (with the make contact not energized, and the break contact energized) (b) Between adjacent contacts (c) Between coil and contact (d) Between two coils of double coil latch type (between set coil and reset coil) (e) Between ground pin and contact pin and between ground pin and coil pin with a relay with a ground pin (5) Breakdown voltage
1 Apply a surge voltage or AC voltage between insulated conductors and confirm that breakdown does not
occur.
2 Use a breakdown voltage tester and apply the specified voltage to the sample for 1 minute.
3 Measure the breakdown voltage at the same pins as those at which the insulation resistance is measured.
6. TERMINOLOGY
Operating temperature range Temperature range in which the stable performances of the relay can be drawn out. Usually, the coil voltage rating is specified as the coil input, and the contact load is specified as the maximum value. Mechanical life Life expressed as the number of operations that can be performed when the nominal coil voltage is applied to the relay with the contacts not loaded and the relay is operated at the rated operating frequency. Electrical life Switching life of the contacts expressed as the number of operations measured when the rated voltage is applied to the relay and the relay is operated at the rated operating frequency with the rated load is applied to the contacts.
Epoxy resin
(3) Life
Case (cover)
Figure 28 Plastic sealing
(4) Contact noise Immediately after the contacts have been closed, the surfaces of the contacts come in contact with each other mechanically and electrically. However, the contact spring that holds the contact is vibrating due to repulsive energy that has been generated when the contacts have collided. At this time, because the contact spring vibrates near the magnetic circuit of the relay, an electromotive force is generated due to magnetic induction. Generally, a peak-to-peak voltage of several µV to several ten mV is generated, which gradually decreases toward zero. This vibration of the spring may pose a problem when the relay is used in a scanning system that switches minute signals at high speeds.
0 Time V1 V0 V0
0 Time
Contact
Contact spring
Contact
Figure 30 Shape of Twin Contact
(6) FCC Part68 This is Part68 of the US communications standards that regulates the terminal equipment connected to public telephone circuits. This standard requires that the relay used in the circuit terminal withstand a certain value of surge voltage and have a certain breakdown voltage. The following figure and table show the specific values of the surge and breakdown voltages. Surge voltage
VMAX.
Condition
t1 (µs) 10 10 2
t2 (µs) 560 160 10
VMAX (V) 800 1500 2500
Figure 31 Surge Voltage Waveform Applied AC voltage Condition 1 1000 Vac (sine wave AC, effective value) Condition 2 1500 Vac (sine wave AC, effective value) The above voltage must be applied (a) between opening contacts, (b) between adjacent contacts, and (c) between the coil and contact of a relay so as to prove that the relay has no problem.