RELAY AND FUNCTION
Relay is a kind of automatic switching component
with isolation function, which is widely used
in
remote control, remote measuring, telecom, automatic
control, integration of machinery and
electrification, electric and electronic equipments.
It¡¯s one of the most important controlling
components.
Generally, relays have the inductive organ
(input part) that can reflect the input value
(such as
current, voltage, power, impedance, frequency,
temperature, pressure, speed, light etc.); have
the executive organ (output part) that has the
capability of switching the controlled circuit
¡°on¡± or
¡°off¡±; between the input and output parts, there
is the medium organ (actuator) that can make
input value coupling-isolation and drive the
output part.
As a kind of controlling component, generally,
relay mainly has the following functions
1) To enlarge the range of control. E.g., when
the controlling signal of a multi-contacts relay
reaches a certain value, according to the different
forms of the contacts, it can synchronously
change over, close or open several circuits.
2) Enlargement. E.g., sensitive relays and medium
relays can control a high-power circuit with
minute controlling power.
3) To integrate signals. E.g., when several
controlling signals are put into a multi-winding
relay in
the stated form, the relay can realize the expectant
controlling function by analyzing the different
signals.
4) Automatization, remote control and monitoring.
E.g., in automatic equipments, the relays and
other electronic components can constitute program-controlled
circuit, realizing the automatic
operation.
TECHNICAL REQUESTS OF MAIN PARAMETERS OF RELAY
1. Requests of mechanical and physical parameters:
To Guarantee the mounting dimension, weight,
the intensity and soldering of the terminals
etc.,mechanical parameters mainly include contact
force, contact gap, contact follow, return
spring force, armature travel, stop plate height
etc.
2. Requests of time parameters:
When controlling the circuits, pickup and dropout
time is usually required. Other time parameters
include armature changeover, contact chatter,
pulse distortion etc.
3. Request of ambient adaptability:
According to the application fields, in order
to guarantee the relay operates reliably, ambient
adaptability items mainly include temperature
(max. and min temperature, temperature cycle,
temperature shock, low temperature storage etc.),
humidity resistance (high humidity at normal
temperature, high humidity at high temperature),
low air pressure resistance, vibration stability
and vibration strength, shock stability and
shock strength, constant acceleration.
In special environment, it also includes salt-mist
resistance, mildew resistance, radiation
resistance, transportation, storage etc.
4. Requests of life and failure ratio:
When relay works under the specified ambient,
specified contact load, and in specified operating
times, the failure times should not exceed the
specified times. The failure refers to the contact
freezing that makes the contact voltage drop
exceed the specified level when the contacts
pick up
when the relay is working.
All the relays that have the requests of established
reliability index have specified class of failure
ratio.
5. Requests of safety specification:
To avoid electric-shock and fire, the product
must accord to the safety stipulation of relevant
country, e.g. CQC of China, UL of America, CSA
of Canada, VDE and TUV of Germany etc.
Not all the relays should reach all the requests.
The technical requests differ from the different
application conditions.
TEST OF MAIN PARAMETERS
1. Pickup and dropout value
The test of non-pickup value, pickup value,
hold value and dropout value should be carried
out
according to the test process drawing (Fig 1)
followed. The process is uniform to both
manufacturers and users. The biggest merit of
the process is that the tested parameters can
be
repeated. It doesn¡¯t indicate that the relay
would be magnetized first and work second when
the
relay is used.
Generally, the pickup voltage of AC relay doesn¡¯t
exceed 85% of the rated voltage, and the pickup
voltage of DC relay doesn¡¯t exceed 75% (some
are 80%) of the rated voltage. The hold voltage
of DC relay is 30%-40% of the rated voltage,
but the hold voltage of AC relay is a little
higher than that of the DC relay. The dropout
voltage of DC relay isn¡¯t less than 10% of the
rated voltage, and under limited low temperature,
it isn¡¯t less than 5% of the rated voltage.
The dropout voltage of AC relay generally is
about 30% of the rated voltage, and under limited
low temperature, it isn¡¯t less than 10% of the
rated voltage.
2. Coil resistance
Coil resistance can be measured by the voltage-current
means and electrobridge means. When using voltage-current
means, the inner resistance of the voltmeter
and ammeter should be lessened as little as
possible and the measuring process should be
as short as possible to avoid the rise of the
coil temperature. The coil resistance is sensitive
to the ambient temperature, so within 1-2 hours
before the testing, the relay should be placed
in the testing ambient and (had better) don¡¯t
energize the coil. The tested value ¡°Ra¡±should
be converted to the value under basis temperature
(normally 20¡æ), the conversion formula is:
Ra=R0[1+a(Ta-20)]
In the formula£º Ta is the ambient temperature£¨¡æ£©
a is the temperature coefficient of resistance£¨the
temperature coefficient of cupreous lead wire
is 0.004/¡æ£©
3. Contact resistance
When measuring the contact resistance of NC
contacts, the relay is on un-energized state;
when measuring the contact resistance of NO
contacts, the relay is on energized state. The
contact resistance can be measured by voltmeter-ammeter
means. When measuring, the contact load (resistive)
should accord with the regulations showed in
table 1. The tested part is within 4mm to the
end of the terminals. The load should be applied
on the contact after it stably closes and cut
off before it breaks.
The international specified load value when
measuring the contact resistance (or voltage
drop).
Application type |
Testing load£¨resistive£© |
CA0
|
¡Ü30mV £¬ ¡Ü10mA |
10mA ¡Á 30mV |
CA1 |
30mV~6V£¬0.01~0.1A |
10mA ¡Á 100mV |
CA2 |
5~250V £¬ 0.1~1.0A |
100mA ¡Á 24V |
CA3 |
5~600V £¬ 0.1~100A |
1A ¡Á 24V |
Note: When there are several application types,
the criterion is the requests of the lowest
application type.
4. Insulation function
Generally, the insulation resistance is tested
by mega-ohmmeter; the tested relay should be
paced on high quality insulating board; the
testing voltage should accord with the technical
requirements of the relay; the minimum value
after the voltage is applied for 2s is the measured
value.
A dielectric strength test should last 1~5s
under the high-tension voltage (110% of the
rated voltage). If any dispute exists, the test
should last 1minute under the rated voltage.
5. Time parameters
The measuring circuit drawing of the time parameters
is showed in figure 2 followed. Other apparatus
and instruments are allowed to use as substitutes,
but the contact load should be resistive. To
measure the operate time, release time and bounce
time, the contact load should be 10mA ¡Á6v (resistive
load); to measure the stable time, the load
should be 50¦ÌA ¡Á 50mV (resistive ). The distinguish
ability of the instruments is 1¦ÌS.
To measure the operate time, the relay should
be energized by the lower limit of the rated
voltage; to measuring the release time, the
energized voltage should be cut off from the
upper limit of the rated voltage. The typical
wave figure is showed in figure 2:
6. Outline dimension
The criterion of outline dimension test is the
outline drawing of the relay. To measure the
dimension of terminal¡¯s position, the correct
measuring position is in 3mm apart from the
holder. When measuring, the outside force applied
shouldn¡¯t bring any damage to the relay.
If there are no special regulations, the measure
mentioned in 6.1 to 6.5 are all carried out
in normal climate conditions: The temperature
is 15¡æ-35¡æ; the relative humidity is 45%-75%;
the air pressure is 86.7~106.7Kpa
GUIDELINES OF RELAY CHOOSING
1. Choosing relay according to the applicative
ambient
The conditions of applicative ambient mainly
refer to temperature (highest and lowest), humidity
(generally refers to the highest relative humidity
at 40¡æ), low air pressure (it can be ignored
if the relay is used under the height of 1000m),
vibration and shock. Besides, the package type,
mounting method, outline dimension and insulating
function are also required. Because the material
and the construction are different, relays bear
different ambient mechanics conditions. The
relay may be damaged if it is used under the
conditions that exceed the specified ambient
mechanics conditions specified by the product
standard. It is feasible to choose the right
relay according to the ambient mechanics conditions
or higher-level requirements.
AC relay isn¡¯t very suited for the ambient that
is sensitive to the electromagnetic or RF interference.
When choosing DC relay, you should choose the
relay with transient suppression circuit. In
the mounting ambient in which the relay is energized
by solid-state components or circuits, or the
ambient is sensitive to peak signals, you also
should choose the relays with transient suppression
circuit.
2. Choosing the relay type according to input
signals
There is no question to choose electromagnetic
relay, temperature relay, time relay or photoelectrical
relay according to the different input signals
of electricity, temperature, time or light.
Here, we specially indicate the choosing of
voltage relay and current relay. You should
choose current relay if the equipment could
provide the coil constant current and choose
voltage relay if the machine could provide the
coil constant voltage.
3. Choosing the input parameter
The input parameter that is tightly connected
to the user is the coil operating voltage (or
current). The pickup voltage (or current) is
the parameter to control the sensitivity, to
judge and examine the relay for the relay manufacturer.
To the users, the pickup voltage (or current)
is just a lower limit of the operating parameter.
The control safety coefficient is operating
voltage (current) / pickup voltage (current).
It is unreliable and unsafe to use the relay
under the pickup values. The ambient temperature
rise, vibration and shock would lead the relay
to operate unreliably. When designing the equipment,
it is not right to use the unload voltage as
the criterion of the relay operating voltage.
The right method is to calculate the actual
voltage regarding the coil as the load, especially
when the inner resistance of the power source
is high. When using transistor as the controller
to switch on or off the coil, the transistor
must be on the on-off state. For the relay that
the operating voltage is less than 6VDC, it
is required to deduct the saturation voltage
drop of the transistor. Of course, it doesn¡¯t
mean that the operating value can be increased
unlimitedly. If the operating value exceeds
the rated value too much, the shock abrasion
of armature and contact bounce times would be
increased; the electrical life would be shortened.
Generally, the operating value is 1.5 times
of the pickup value; the error of the operating
value is in the range of ¡À10%.
4. Choosing the contact type and capacity according
to the load
It is verified by practice that about 70% of
the faults are because of the contact, which
indicates that correctly choosing and using
the relay contact is very important.
The contact form and amount of sets should be
determined by the actual conditions of the controlled
circuit. The common contact arrangements are
showed in table 6. Because of less amount of
bounce times when the circuit is switched on
and larger amount of compensation after ablation,
the load capacity and reliability of the make-contacts
and make-contact in changeover contacts is higher
than that of the break-contacts and break-contact
in changeover contacts. So the circuit can adjust
the contact position to choose make contacts
as long as possible.
It is very important to determine the parameters
according to the load capacity and characteristics
(resistive, inductive, capacitive, lamp load
and motor load). It is wrong to consider that
small contact-switching load is certainly more
reliable than large contact-switching load.
Generally, it is best that when the switching
load is under the rated voltage, the current
exceeds 100mA and less than 75% of the rated
current. If the current is less than 100mA,
the contact carbon collection will increase
and thus the reliability will decrease. So 100mA
is regarded as the experiment current, which
is the examined content to the world relay manufacturers
to estimate the relay manufacturing technics
level and conditions according to the professional
criterion. Because most relays don¡¯t have the
low level switching capability, when ordering
the relay with switching load less than 50mV¡¢50¦ÌA,
the user must give special note or ask the manufacturer
to assist to choose the right type of relay
if necessary.
The rated load life of relay is the operating
times of relay under rated voltage, rated current
and resistive load. When the voltage exceeds
the rated voltage, the relay can be chosen according
to the contact load curve. When the characteristics
of the load changes, the contact switching capability
will change, and the user can change the load
current according to table 2
Resistive
current |
Inductive
current |
Motor
machine current |
Lamp
current |
Least
current |
100% |
30% |
20% |
15% |
100mA |
Only resistive rated load is noted on the cover
of relay. Please look up other kind of rated
load in the detailed technical information,
and the surge current is showed in table 3.
If the relay is used in occasions of polar changeover
load or phase changeover load,the three-position
contact of K type (in table 6) is the best choice.
Don¡¯t choose the two-position contact of Z type
unless the relay is clearly prescribed to be
used in three-phase AC load occasion. Or, with
the increase of the operating times, the burning
arc will increase, so the power source circuit
may be shortened by Z type contacts. When switching
un-synchronous single-phase AC load, the phase
dispersion will exist, so the contact rated
current should be 4 times of the load current,
and the rated voltage is 2 times of the load
voltage. The contacts that is suited for AC
load isn¡¯t always suited for the load switching
between several source phases. When necessary,
relevant experiment of electric life should
be done.
Types of loads |
Surge current |
Surge time |
Remarks |
Resistance |
Steady current |
|
L¡Ü10-4H or cos¦Õ=10-0.01 |
Solenoid |
10~20 times of steady current |
0.07~0.1 |
Treated as inductive load,
if¦Ó=L/R<10-4S, it can be treated as resistive
load. |
Motor |
5~10 times of steady current |
0.2~0.5 |
Can replace the motor load
with 5~6 times current of resistive load. |
Incandescent lamp |
10~15 times of steady current |
0.34 |
|
Mercury lamp |
About 3 times of steady current |
180~300 |
|
Neon lamp |
5~10 times of steady current |
¡Ü10 |
|
Sodium lamp |
1~3 times of steady current |
|
|
Capacitive load |
20~40 times of steady current |
0.01~0.04 |
Long transfer wire¡¢filter¡¢power
source etc. can be regarded as capacitive
load. |
Transformer |
3~15 times of steady current |
|
|
Electromagnetic contactor |
3~10 times of steady current |
0.02~0.04 |
|
APPLICATION OF RELAY
The product reliability generally refers
to the operating reliability. It is defined as:
the ability of accomplishing the specified function
under prescribed conditions and in prescribed
time. It consists of intrinsic reliability and
application reliability. The intrinsic reliability
is determined by product designing and manufacturing
technique, and the application reliability is
concerned with the correct application of users
and the services provided by the manufacturer
before and after selling
When using relay, the user should pay
attention to the following items.
1. Coil applied voltage
It is best to choose the coil applicative voltage
according to the rated voltage in design, or choose
the voltage according to the temperature rising
curve. Using any coil voltage that is less than
the rated voltage will affect the operation of
the relay. The coil operating voltage refers to
the voltage that is applied between the coil terminals.
The voltage value between the two terminals must
be guaranteed, especially when using enlargement
circuit to energize the coil. Whereas, it will
also affect the relay characteristics if the applied
voltage exceeds the highest rated voltage. Exorbitant
voltage will bring exorbitant coil temperature
rising, especially in high temperature ambient.
Exorbitant temperature rising will damage the
insulating material and affect the working safety
of relay. For magnetic latching relay, energizing
(or return) pulse width should not less than 3
times of the operating (or return) time, otherwise,
the relay would be left on the middle-position
state. When using solid-state components to energize
the coil, the components dielectric strength must
be above 80V, and the leakage of current must
be as little as possible to ensure the relay to
release.
Energizing power source: Under 110% of the
rated current, the adjusting ratio of the power
source is less than 10% (or the output impedance
is less than 5% of the coil impedance), the
wave voltage of the DC power source is less
than 5%. The AC wave is sine wave; the waviness
coefficient is between 0.95~1.25; wave distortion
is within ¡À10%; the frequency change is within
¡À1Hz or ¡À1% of the specified frequency (choosing
the bigger value). The output power should not
less than coil power consumption.
2. Transient suppression£º
At the moment when the coil power is stopped,
peak-inverse voltage that is more than 30 times
of the coil rated voltage is produced on the
coil, which is harmful to the electronic circuit.
Generally, the peak-inverse voltage is suppressed
by transient suppression £¨cutting-peak£© diode
or resistance to limit the peak-inverse voltage
within 50V. But the diode in parallel connection
will delay 3~5 times of the release time. If
the request of the release time is high, a suitable
resistance in series can be putted with and
at one end of the diode.
3. The power supply to relays in parallel connection
and series connection
When several relays in parallel connection are
supplied, the relay that the peak-inverse voltage
is higher will release power to the relays that
the peak-inverse voltage is lower. The release
time of the relay will delay. So the relays
in parallel connection should be controlled
separately to eliminate mutual influence.
The relays with different coil resistance and
power can¡¯t be used in series, otherwise, the
relay that the coil current is higher in the
series circuit can¡¯t operate reliably. Only
the relays of the same specification can be
used in series, but the peak-inverse voltage
will be increased and the peak-inverse voltage
should be suppressed. Resistance in series can
be used to bear the part voltage that exceeds
the rated voltage of the coil according to the
ratio of the divided voltage.
4. Contact load
The load applied to the contacts should be accordant
to the rated load and characteristics of the
contacts. A load that is not applied according
to the rated value range will cause problem.
The relay that is only suitable for DC load
can¡¯t be used in AC occasions. The relay that
can switch 10A load can¡¯t always reliably operate
in low level load (less than 10mA¡Á6A) or in
dry circuit occasions. The relay that can switch
single-phase AC power source isn¡¯t always suitable
to switch two single-phase AC loads that aren¡¯t
synchronous; the relay that is only specified
to switch the load of AC 50Hz£¨or 60Hz£©can¡¯t
be used to switch AC load of 400Hz.
5. Parallel and series connection of contacts
The contacts used in parallel connection can¡¯t
increase the load current, because the operating
times of several sets of contacts are absolutely
different; that is to say, there is still only
a set of contacts switching the increased load.
This would damage or weld the contacts and make
the contacts can¡¯t close or open. The parallel
connection of the contacts can decrease the
misplay of ¡°break¡±. But the parallel connection
of the contacts would increase the misplay of
¡°freezing¡±. Because the misplay of ¡°break¡± is
the main pattern of invalidation of contacts,
the parallel connection can increase the reliability
and can be used on the pivotal part of equipments.
But the applied voltage should not exceed the
highest operating voltage of the coil and should
not less than 90% of the rated voltage, otherwise,
the coil life and the applicative reliability
would be damaged. The series connection of the
contacts can increase the load voltage. The
amount of the contact sets is equal to the times
that the load voltage can be increased. The
series connection of contacts can decrease the
misplay of ¡°freezing¡±, but it would increase
the misplay of ¡°break¡±. Anyway, when using redundant
technology to increase the operating reliability
of contacts, the characteristics and size and
the failure mode of load must be considered.
6. Switching speed
The switching speed should not exceed the reciprocal
of 10 times of the sum of operating and release
time (times/s), otherwise, the contacts can¡¯t
switch on steadily. Magnetic latching should
be used under the pulse width specified in the
technique criterion, or the coil may be damaged.
MOUNTING OF RELAY
. Protection of the terminals
If the relay is soldered on PCB, the distance
among the holes must be correct, and the diameter
of the hole should not be too little. When it
is necessary to pull or turn the terminals,
the terminals must be fixed at the position
3mm from the relay holder. The terminals that
the diameter is more than 0.8mm can¡¯t be pulled
or turned. There should be a distance exceeding
0.3mm between the holder and the PCB, which
can protect the terminals from outer damage
and be convenient for the cleaning solvent to
flow out and volatilize of after soldering.
To the soldering hole and soldering hook types
of terminals, when soldering the joining lead
and the lower lead, twisting or drawing to the
lead must be prevented, otherwise, the terminals
may become flexible. As for screw and bolt mounting
terminals, the moment of torsion should less
than the values listed in table 4 when mounting.
Unit£ºN?M (Table 4)
Specification
of bolt |
M2.5 |
M3.0 |
M3.5 |
M4.0 |
M5.0 |
M6.0 |
Used
for connection |
With
heads |
0.40 |
0.50 |
0.80 |
1.20 |
2.00 |
2.5 |
Without
heads |
0.20 |
0.25 |
0.40 |
0.70 |
0.8 |
|
Used as terminal |
0.40 |
0.50 |
1.14 |
2.28 |
4.00 |
8.00 |
Used as mounting
parts |
¡ª |
1.00 |
2.00 |
4.20 |
¡ª |
|
Note: If the relay falls to the ground when mounting,
the inner parts may be damaged because of the
strong shock. The relay can¡¯t be used until it
is examined again.
2. Soldering and cleaning
The terminals should be soldered with the litmusless
resin-type flux, not acidic flux. After soldering,
the relay must be cleaned and dried. The wattage
of the soldering iron is appropriate between 30~60W;
the highest tip temperature is appropriate between
280~330¡æ; the soldering time is 3s max. In automatic
soldering , the temperature of molten solder is
260¡æ; the soldering time is 5s max. When soldering
and cleaning, the un-sealed relay must be protected
to avoid polluting the inner construction by the
flux and cleaning solvent; the hermetic and washable
plastic-sealed relays can be immersed to the cleaning
solvent when cleaning.
3. Preventing enlargement of vibration
For the relay with requirements of vibration resistance,
choosing the suitable mounting method can prevent
or lessen the enlargement of vibration. The best
means is to mount the relay at the position that
the direct of the vibration is vertical to the
movement direct of the armature. Avoid choosing
the relays mounted with top crew bolt or bracket.
4. Adjacent mounting method of several relays
When several relays are mounted on a PCB or a
card rack, abnormally high temperature may result
from the combined heat. The relay without magnet-screen
cover may operate abnormally because of the magnetic
influence. The question can be settled by the
means of mounting the relays with sufficient space
between them or mounting other components (that
can not produce strong heat and magnetic field;
can bear certain influence of heat and magnet)
between them.
RELAY PROTECTION
1. Coil protection
If possible, the coil and core should be kept
at the same potential level whenever the coil
is ¡°on¡± or ¡°off¡±, to avoid the electrochemical
corrosion.
2. Contact protection
There are many protective circuits to protect
the contact. For inductive load, diode in parallel
connection with the load is generally used to
eliminate sparkle; RC absorption network or
voltage-sensitive resistance in parallel connection
with the contact is used to protect the contact.
To capacitive load or lamp load, little power
resistance or RL suppressing network in series
is generally used in the loop circuit to suppress
the shock from surge current.
|