In the production process surveillance and the
control needs to use the many kinds of automated measuring appliance,
the computer and the corresponding implementing agency, mutually
transmits both has the weak millivolt level small signal, and has
dozens of volt big signal, even also has reaches as high as several
kilovolts, several hundred ampere signals. Says from the
frequency, has direct current low frequency, also has the high
frequency pulse. Mutual disturbance between the equipment, the
measuring appliance of becomes the question which in the system
debugging must have to solve. Besides the electromagnetic
screen, solves each kind of equipment, the measuring appliance "",
namely the signal reference point potential difference, is the scene
debugging important question.
1. isolation two principles
The signal wants the integrity transmission, must
solve the different equipment, reference point potential difference
between the measuring appliance signal. The idealized situation
is all equipment, the measuring appliance signal has a common
reference point, namely altogether has "". Further says, all
equipment, between the measuring appliance electricity reference point
the potential difference is "zero". In the actual environment,
this point is nearly impossible. Inside this the loss of voltage
which besides each equipment, the measuring appliance "" the between
segment resistance produces, still had each kind of equipment, the
measuring appliance the disturbance which received in the different
environment is different, as well as the wire contact underwent
风吹雨淋, caused the contact quality drop and so on many factors,
caused each "" between to have the difference. Take the chart
one as the example
Chart PLC meets the measuring appliance
schematic drawing with outside
Chart center two scenes equipment 1 #, 2 # to the
PLC transmission signal as well as PLC to two scenes equipment 3 #, 4
# send out the signal. Supposes the transmission signal is
0-10VDC. Ideal situation, PLC and two scenes equipment 1 #, 2 #
"" electric potential closely coincide. In the transmission
process has not disturbed, PLC receives correctly.
But 如前所, two scenes equipment usually have "" the
potential difference Gives an example to say, 1# equipment ""
and PLC "" electric potential same, the 2# equipment electric
potential reference point "" electric potential is higher than 0.1V
them. Such 1# equipment for the PLC signal is 0-10V, but the 2#
equipment for PLC was 0.1V-10.1V, the error produces.
Simultaneously 1# the,2# equipment "" the line in the PLC
convergence joint, exerts the 0.1V voltage in the PLC line, has the
possibility to damage the PLC local circuit board line, simultaneously
can demonstrate the wrong data.
"" Causes the question repeatedly has the appearance in the
scene debugging. For example some large-scale building materials
company in the production line monitoring equipment, has used overseas
some company PLC and domestic some factory holding. This PLC
each data acquisition board is composed by eight channels, eight
channels altogether use 12 A/D, after the process transformation
digital signal to transport to isolate by 12 light pairs constitution
disconnector realization and the main engine, but between its eight
channels input has not certainly isolated. When input signal,
each channel alone inputs to the gathering board is normal. When
simultaneously inputs two or are many to two exterior signals,
demonstrated the numeral jumps madly, the breakdown is unable to
remove. Also like astronautics some department uses K 热偶 to
take sensor test engine each temperature, with above similar, when
tests a spot all normal, when turns on two spots to the main engine or
more spots, the demonstration temperature obvious is wrong.
After these two kind of situations use disconnector, the
question solution work is normal.
The disconnector therefore can play this role, is because it has
causes the input/output the characteristic which completely isolates
on the electricity. 换句话讲, between the input/output "",
the external signal no matter is 0-10V not together, or is bringing
altogether mold disturbing voltage 0-10V after the isolation is 0-10V.
After namely the isolation the new establishment "" with the
external instrumentation, the measuring appliance "" has not related.
Is precisely as a result of this reason, also realized has input
meets between the equipment measuring appliance signal to outside PLC
main engine many to isolate, namely between them did not have ""
relations.
On spoke face-to-face the input signal and the PLC isolation,
same PLC also has the similar phenomenon question to the external
instrumentation output signal, uses the disconnector to be able to
achieve solves the question goal.
Another kind frequently meets the situation is requests a signal
both to be able to demonstrate the measuring appliance transports the
signal, and can transmit for such as the frequency changer and so on
equipment, like this has the possibility to produce between two
equipment 互扰. By now requested between two outputs also was
the isolation. Recommendation use 隔离?signal distributor.
It can realize the input signal to isolate with the external
instrumentation, simultaneously realizes between the receive signal
device to isolate. Like chart 2.
Chart two 隔离?signal distributors
model application
In summary, the solution "" the question needs to
follow two principles. First: The external instrumentation
and the central processing system (for example PLC, DCS) between must
carry on the electricity to isolate. Second: External
instrumentation signal (regardless of is to central processing system
transmission signal external instrumentation to or receive signal
external instrumentation) between must realize the mutual electrical
isolation. The system installment followed these two principles
to be able completely to overcome because "" between difference
introduction disturbance.
The majority disconnector all wants the sur- work power source,
generally is DC 24V or AC 220V. This
power source when for input, output part power supply must guarantee
on the electricity/outputs two modified quarantines with the input.
Between this kind of input/output/sur- work power source
completely mutually isolates the component is called three isolation
or all isolates the component. Theoretically speaking, this
power supply way no matter disconnector quantity how many, may use a
power source power supply, cannot introduce the disturbance.
Such product conforms to the above two principles.
2. bases connections choice product
The industry scene most common signal is
4-20mA□p0-10V, regarding such as physical quantity and so on
pressure, temperature, current capacity also must process
4-20mA□p0-10V the signal in order to computer processing.
Transforms these physical quantities for the measuring appliance
is called with 4-20mA□p0-10V the signal equipment -- changes
delivering. The chart three has produced as the sensor isolation
temperature changes the delivering application continually graph take
Pt100. It manifests the temperature change by the resistance
change, thus the scene ties line resistance can introduce the error.
Generally says looks like WS9050□pWS2050 this kind to change
delivering all to have the long-line compensatory function, can
eliminate the lead wire resistance introduction the error and has the
linearized function, guarantees the precise transformation.
Looks like WS2050 this kind of two-wire system to change
delivering, its power source AND output altogether "", has not
isolated. When many Pt100 transports by way of multichannel
WS2050 to PLC, although outputs altogether uses a 24V power source, so
long as outputs receives has the common reference point the simulation
quantity input board, this kind of connection conforms to two
principles which this article above pointed out, solved has been
different "" the introduction perturbation. Needs to pay
attention: Multichannel WS2050 receives different PLC to have to
use respective 24V power source.
In view of changes the delivering isolation also to have
another way, the sensor and changes delivering is a body but also must
lay aside in the scene assigned location. This time generally
places the disconnector in the master control room cabinet, changes
delivering by the cabinet in disconnector for the scene to match
delivers the power source. The chart four has produced in view
of the different connection two kind of products continually graph.
Which one kind uses to have to decide according to the scene
situation.
The scene debugging also can appear the measuring appliance
connection not to match. For example the scene transmitter
installation for 四线?changes delivering output 4-20mA, but the
receiving end 4-20mA connection is two return routes power supplies
way, if directly will connect creates the power source conflict.
The solution is uses the disconnector the 4-20mA receive and the
isolation which comes the scene, installs a allocated-use circuit in
the disconnector output part to use to match the connection two return
routes power supplies way. This kind of disconnector also may
process from scene 0-10V, voltage electric current signal and so on
0-5AAC.
Outside the general 4-20mA electric current signal disconnector
needs to meet the work power source. Here recommends one kind
not to need other to add the power source again disconnector WS1562.
Like chart six
The WS1562 most major characteristic is does not need
the external power supply, the wiring simple and direct □p power loss
low □p reliable performance is high, the multichannel connection
conforms to the above two principles.
The chart seven is WS1562 in the output is under the
20mA condition, output load and input end voltage relations curve.
VIN expresses in the input end voltage □pRL expression output
load resistor □pVO expression output load resistor voltage.
The chart eight produces two kind of passive disconnectors
output load to a linear curve, solid line description performance is
better, output load resistor RL from 0 Omega -500 Omega change, linear
all in 0.2%.
3. main parameters selections
The choice disconnector besides must around
determine the function □p attention adapts the end connection, still
had the precision □p power loss □p noise □p insulation strength □p
main line communication function and so on many parameters cautious to
need the user to elect.
The precision is the count for much parameter. Are very
many with its related department's parameter. The time drifting
and the temperature drifted two parameters to indicate the precision
stable degree, slightly requested these two parameter values to be
better.
Another has the influence parameter to the precision is a noise.
Because the disconnector generally uses DC/DC to produce
isolates the power source for the product internal circuit power
supply, but the input signal also must first modulate the pulse (light
occasionally transformer) then to demodulate again after the isolation
belt the output. As the core disconnector also has the pulse
signal take CPU. These work pulses frequencies 率多 in 20KHZ ~
100KHZ scope. Its edge steep □p overtone rich, is very
difficult to the signal pollution to eliminate. If noise higher,
the data acquisition gathering signal error is big. Therefore
the noise peak value and the energy smaller are better.
The electrical energy which the power loss is refers to when
disconnector work consumes, it involves the quantity of heat which
produces to the product. This parameter and the product
long-term use reliability has the close relation.
According to the analogous circuit test, the different power
loss the quantity of heat which produces in the product shell
different, causes in the shell 温升 to be also different. The
product is at under the active status, in the product shell compares
outside the shell the ambient temperature to have to outdo 10 ?~ 30
? If radiates is not good, possibly elevates 50 ?above.
If shell in vivo hyperpyrexia, composition product primary
device in high temperature long lasting work, this can have the
important influence to the product performance. The long time
high temperature environment causes the operational amplifier
parameter transformation □p resistance resistance number change □p
electric capacity leakage to increase and so on, this will cause the
product performance to drop, even will cause the product expiration.
Therefore the user must pay attention to power loss this
parameter in the selection, especially bigger □p installs when the
amount used a density higher □p radiation is not good, power loss
this parameter especially reveals importantly.
The isolation 端子 design miniaturizes day by day, then the
miniaturized goal little occupies the space, should allow the user
crowdedly to install, crowded installment on existence radiation
question. 换句话讲, must reduce the product power loss,
reduces the product interior temperature, this enhances one of product
reliable premises.
The majority of disconnectors use the guide rail installment,
the wiring use 端子 the wiring, this kind of disconnector usually is
called the isolation 端子, is suitable installs in the cabinet, its
wiring opens trades conveniently.
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