Understanding the function, characteristics, principle, classification and selection of signal isolators (III)

The principle of the signal isolator:

The principle of the signal isolator is to convert the signal of the transmitter or the meter through the modulation of the semiconductor device, and then realize the isolation conversion by the optical or magnetic sensing device, and then perform the demodulation and conversion back to the original signal before isolation, and simultaneously isolate the signal. The power supply is isolated to ensure absolute independence between the converted signal, power supply and ground. At the same time, the interference signal superimposed on the measured value is filtered, and the signal is matched according to the input and output requirements of the control system. Therefore, isolation, amplification, filtering and matching are the functions of the signal isolator.

Some DCS modules have optical isolation function, which can meet the normal working requirements in some systems. However, the system cannot always be in normal working condition. In case of accident, the device is damaged. Replacement of the isolator is more time-saving and cost-saving than replacing the DCS module. Therefore, Yikongjun still needs to determine whether to install the isolator according to the actual situation.

Classification of signal isolators:

The signal isolators are divided into active signal isolators and passive signal isolators.

Active signal isolators:

The active signal isolators are powered by separate power supplies to ensure excellent isolation of the isolators. The modules require active signals on the input side and filtered and amplified signals at the output, depending on the application. Isolated from each other. Active signal isolators include three-terminal isolation, input isolation, and output isolation.

1.Three-terminal isolation

Three-terminal isolation requires only one power supply. This power supply is isolated from the measurement circuit. The modules isolated by this technology do not interfere with each other. The components connected to the input, output or power supply do not interfere with each other. Electrically isolated from each other.

2.Input isolation

Modules using this isolation technology should protect the electronic devices connected to the output side (such as the controller's input card) from the field. Therefore, the input and the equipotential output are electrically isolated from the power supply.

3.Output isolation

Modules using this isolation technology should protect the electronic devices connected to the input side (such as the output card of the controller) from various disturbances on site. Therefore, the output and the equipotential input and the power supply are electrically isolated.

Passive signal isolators:

The passive signal isolator provides an additional and substantial convenience. It does not require additional power supply. The operating power of the module is provided through the input or output loop. The internal circuit consumes very little current and does not affect the correct signal. transmission. According to the power supply mode of the signal isolator, the input side power supply, the output side power supply, and the passive power supply are divided.

1.Input side power supply

With this isolation technique, these passive signal isolators draw the required energy from the active input loop (such as an electromagnetic flowmeter or control system output card) for signal transmission and electrical isolation, and the output side provides a processed current signal. Used for control or adjustment.

2.Output side power supply

With this isolation technique, these passive signal isolators (output side gain energy) draw the required energy from the active output loop (preferably from the control system input card with the auxiliary power supply) for signal transmission and power. isolation.

Passive Feed Isolator:

With this isolation technique, these modules take the required energy from the active output loop for signal transmission and electrical isolation, and the passive feed isolator supplies this additional energy from the output loop to a connection on the input side. A passive detection probe (such as a pressure transmitter) that emits an active signal by means of the supplied energy, is electrically isolated by a passive feed isolator and is output from the output side.

How to choose the isolator:

The isolator is located between the two system channels, so the choice of the isolator must first determine the input and output functions, and at the same time make the isolator input and output mode (voltage type, current type, loop power supply type, etc.) adapt to the front and rear end channel connection 1:3 mode. In addition, there are many important parameters such as accuracy, power consumption, noise, insulation strength, bus communication function, etc. related to product performance, such as noise and accuracy, power consumption and reliability, which require careful selection by users. In short, the application, reliability, and product cost performance are the main principles for selecting isolators.

On the basis of providing optimal electrical isolation, YR9000 series products integrate more technologies and many convenient use features. The signals after the reliable isolation will be converted and transmitted with high reliability, which greatly simplifies the system structure. And greatly reduce the construction cost and I / O module costs, can increasingly meet the growing industrial automation of the signal strict isolation transmission requirements, and in some important industrial applications.