Common applications for analog output

The analog output is basically used in industrial control applications to control the executive equipment of the industrial scene, such as controlling the opening of the valve, controlling the speed regulation of the frequency converter, and so on. The analog quantity is a common signal point in the industrial control industry. Its function is to convert the value of a physical quantity into an electric signal. The electric signal can be divided into a voltage signal and a current signal.
In industrial production, especially chemical production, many regulating valves are used in the technological process. The regulating valve is a common valve whose valve opening can be adjusted from 0-100%. During the production process, we need to adjust the fluid The speed, or other parameters, to control the valve opening, which requires the use of analog output for control.
In the DCS system or PLC system, there are modules with analog output. The module can be selected according to actual work needs, whether it is current or voltage. The current type is commonly used for 4-20mA, and the voltage type is commonly used for 0. -10V, and current type and voltage type are more commonly used 4-20mA current type, because the current signal attenuates less than the voltage signal, and when the signal is zero, the current is 4mA, while the voltage type is 0V, so We cannot judge whether the signal is a true zero point or a disconnection due to a fault.
Our analog output range corresponds to the stroke of the actuator. In the system setting, you can set the positive and negative action between the actuator and the system. The positive action corresponds to the increase in the valve opening when the current increases. The opposite effect is that the current increases and the valve opening decreases accordingly. When the positive action is selected, 4mA corresponds to the minimum valve opening, and 20mA corresponds to the maximum valve opening.
In the wiring process, the general regulating valve is a two-wire system, such as ABB valve actuator, which is a two-wire connection method, and the signal line and the power line are combined into one. To control the inverter, the inverter is generally used in motor speed control, and the most commonly used method for the frequency setting of the inverter is analog input.
The analog input interface of the frequency converter can support 4-20mA current signal and 0-10V voltage signal according to the design of the manufacturer. In the setting of the frequency converter, we can compare our analog quantity range with our actual control requirements. The motor speed is matched. For example, our 4mA current value corresponds to 0Hz of the inverter, which is the 0 speed of the motor, and 20mA corresponds to the 50Hz of the inverter, which is the rated speed of the motor.
In the speed control of the frequency converter, we mostly use it for constant pressure or constant speed control. For example, for a constant pressure water supply system, we can use two ways to set the analog quantity, one is directly using a pressure transmitter The output is connected to the analog quantity setting of the inverter. Another way is to control the inverter through the modulus output of PLC. The connection between the analog quantity and the inverter should consider preventing interference, using shielded cables, and both ends must be reliably grounded, because the inverter will produce harmonics during operation, which will affect the signal quality of the analog quantity.
The above two are just common use occasions for analog output, and more and more analogs are used in industrial control. In the process of use, signal attenuation, interference and other factors must be fully considered.