Safety barrier and isolator lightning protection

The lightning protection grid has a withstand voltage of only several tens of volts. In addition to the power supply terminal, the lightning protection grid is placed on other ports of the safety barrier (isolator), which will reduce the withstand voltage between input, output and power supply from 2500V to several ten volts, so that the safety barrier can not meet the pressure index specified in GB3836.4-2000 standard, the isolator can not meet the insulation requirements of the corresponding standard.

The following four points are for the reference of the lightning protection requirements under the premise of ensuring that the safety barrier (isolator) meets the standard specifications.

All ports to ground: In addition to the power port (grounded), the safety barrier (isolator) input and output lightning voltage between the ground, if less than 2500V RMS / one minute, with effective resistance (not damaged) ).

Between insulated ports: lightning strike voltage or surge voltage between the power grid (isolator) power supply, input and output. If it is lower than 2500V RMS / one minute, it also has effective resistance (not damage).

Between non-insulated ports: no lightning strike voltage is generated between the two terminals of the safety barrier (isolator) power supply, input and output self-loop (the distance between the conductors is very short, and the impedance is very low. Space electric field). However, there is the possibility of accidental impact and misconnection to a higher voltage. Therefore, there are only transient and normal clamp protection requirements. The protection circuit acts between the ports themselves and is insulated from other circuits and the ground. (For the port anti-surge and clamp protection parameters, see "Protection 5, Port Protection."

Power supply to ground: It is completely feasible to configure the lightning protection grid between the power supply (grounded) and the safety barrier (isolator), but it is not necessary to configure the lightning protection circuit in each safety barrier (isolator); The lightning protection grid and the powered instrument can meet the lightning protection requirements of the power grid to the ground.

The safety barrier and the lightning protection grid are safety instruments with different action points. One is to prevent the dangerous gas stored in the site from exploding, and the other is to protect the instrument itself from damage. In comparison, explosive gases are relatively more harmful. There are currently no standards and installation specifications for the connection of the two products, design, manufacture, and selection of products in accordance with existing standards, strict implementation of safety barrier use and installation standards, and is the manufacturer of safety barriers (isolators) (including users). A good and harmless choice.


Indicator verification

1.Process flow and reliability verification

The initial measurement of the product is placed in the front part of the production process. After the initial measurement, it is then subjected to processes such as cleaning, sealing, spraying, drying, aging, and high-pressure impact. After the completion of the above procedures, the inspection is directly delivered, and the difference from the initial measurement data is measured, and correction is prohibited in the process. Verify the product's ability to withstand harsh environments with high impact strength processes.

2.Do not set the zero point and full potentiometer, eliminate all design and process debugging points.

In the process flow, the original zero and full scale original offset value <±3.2μA (0.02% FS) under no adjustment conditions. Can not adjust. (Before leaving the factory, you can also use a large resistance resistor to quickly correct at the initial measurement to achieve higher precision.)

The “no commissioning” process eliminates the possibility of manually adjusting the metering of interventional products, requires single-valued and refined control, and is an effective assessment of design, materials and processing quality.

(Note: Zero and span potentiometers are still reserved in the S series to meet special requirements)

3.Solid isolation

According to GB3836.4-2000, the creepage distance between intrinsically safe and non-intrinsically safe circuits is >3.3mm (under the coating), and the <3.3mm between the intrinsically safe and non-intrinsically safe windings of the transformer is used. 1mm solid isolation, with a compressive strength between each winding > 2500V rms / 1 minute.

4.The use of process protection

Input impact protection includes:

Short circuit, open circuit, misconnection, and misconnection,

shock and interference during operation,

the environment has high and low temperature difference and humidity difference.

The precision of running for a long time or shelving.

Output impact protection includes:

Power consumption and heat limitations when it fails,

power consumption and heat limitation under working conditions,

high heat limit caused by short-circuit distribution and automatic load output open circuit,

Limitations on the interference of the output of the trusted object and the surrounding environment.

The safe value limit of the output energy.