The use of signal isolators in water treatment control systems

Jiangsu Jiangyin 202206 of Renyunye Ankrui Electric Co.
, Ltd.
Abstract: In the water treatment control system, the non-electric analog sensor of the control and monitoring module uses the wiring method of signal isolator to reasonably solve the problem of safety and relative independence of the power supply of the relevant analog sensor, ensures the relative isolation of the power supply, analog acquisition module and output module of the monitoring module, reduces the probability of burning and damage to the template that may be caused, and improves the accuracy of analog signal measurement and anti-electromagnetic interference.
At the same time, it also solves the problem
of limitations due to some non-power installation conditions on site.
Keywords: signal isolator; Water treatment; Analog sensors; 0: Overview In the water treatment monitoring automation system, some analog signals need to be monitored, including electricity analog signals (such as current, voltage, power, etc.
) and non-electricity analog signals (such as pressure, water level, flow, etc.
).

The power analog signal is provided by the transmitter, which can generally output an isolated 4~20mA signal without external signal isolator
.
The working power supply of non-electric analog signal sensors is generally taken from the DC24V power supply module provided by automation system equipment, and most of them are not isolated
.
In order to achieve the safety, stability and relative independence of the power supply of the relevant analog sensors of each control and monitoring module, reduce the probability of breakdown or burning of the power template due to the external short circuit of the working power supply loop of an analog sensor, and endanger the operation safety of the automation system of related equipment, especially for those used in process control that need to implement the threshold alarm, action shutdown and important equipment exit operation of analog sensors The use of signal isolators is a beneficial choice, otherwise there is a possibility of misoperation.
It is not conducive to the safe and stable operation of the entire system, and even causes unnecessary losses
.
1: Analog sensor wiring method type In the water treatment automation control system, generally need on-site pressure, water level, flow and other non-electric signals for measurement and monitoring, often used pressure sensors, water level sensors, flow sensors, etc.
, these non-electric sensors are divided into 2-wire system, 3-wire system, 4-wire system, all need to provide external working power, in order to ensure the safety of the power supply generally use DC24V, the commonly used way is to use DC24V power supply
provided by the relevant control system equipment 。 The entire water treatment automation control system needs to monitor a large number of sensors, pay attention to its importance and ensure the safety of the field control unit, generally provide independent DC24V power module
.
As a bridge between the sensor and the PLC, the signal isolator not only improves the analog signal measurement accuracy, anti-electromagnetic interference ability, and electrical isolation safety performance, but also can reasonably solve the problem of
sensor power supply safety and relative independence 。 Type of wiring method of the sensor The two-wire system is the simultaneous transmission of DC4-20mA standard signals by two wires; Three-wire system is a wire at the positive end of the power supply, a wire at the positive end of the signal output, the negative end of the power supply and the negative end of the signal share a wire, used for voltage reference points and current loops, most of its power supply is DC24V, and the output signal has DC4-20mA standard signal; The four-wire system means that the power supply circuit and the signal loop are independent, separated by an isolation circuit, two wires are responsible for the supply of power supply, and the other two wires are responsible for output signals (such as voltage, current, etc.
).

。 1.
1 Application of signal isolator in analog sensor wiring The working power supply and analog signal input of the sensor do not adopt reasonable isolation measures, which may cause hazards: when the cable or sensor field joint is short-circuited, or when the sensor installed outdoors is overvoltaged by lightning, it will endanger the operation safety of the power module and analog acquisition module on the screen of the control and monitoring system, which may cause the template breakdown or burning, which will seriously affect the operation
of the control and monitoring system 。 At the same time, for 2-wire, 3-wire and 4-wire sensors, there is no reasonable isolation between the power supply and the signal, and its measurement accuracy and anti-power frequency electromagnetic interference ability are greatly reduced, and its measurement accuracy and anti-interference ability will also be affected
.
In recent years, a number of large and medium-sized water treatment systems in China have adopted the wiring method of signal isolator in the power supply and signal loop of non-electric analog sensors to solve and avoid the above problems
.
2: BM100 signal isolator BM100 series signal isolator in industrial production to increase the load capacity of the instrument and ensure that the instruments connected to the same signal do not interfere with each other, improve electrical safety performance
.
The BM100 signal isolator input supports three input modes, compatible with the three wiring methods of the sensor, and isolates the input signal for output and safe transmission to the secondary instrument or PLC/DCS for use
。 BM100 signal isolator wiring diagram BM100 series signal isolator appearance diagram 2.
1 Technical parameters 2.
1 Application examples Due to the limitation of the installation conditions of non-electric sensors in the water treatment site of a group, its analog output signal needs to be expanded to solve the problem of
1 channel 4~2OmA analog signal transmitted to 2 different control and monitoring systems at the same time 。 A single DC4~20mA analog expands the output signal of dual DC4~20mA, which reasonably realizes the relative independence
of the water treatment control and monitoring system.
This method has high isolation strength, strong load capacity, simple installation and wiring, stable operation, safety and reliability, and solves the problems
caused by the installation of sensors in the water treatment field.
Signal isolator application diagram 3: Conclusion The above non-electric analog sensor adopts the wiring method of signal isolator, which is applied in the water treatment automation system, and has achieved good results, and has been applied in a group water treatment, which has played a good demonstration role
in improving the level of water treatment automation control and monitoring.
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