The electrical supply of any modern measuring system is based on a 24V power supply. Without the participation of this element, it is impossible to imagine the operation of any current loop. The principle of its operation is as follows: all electronic devices are assembled sequentially in one large ring, through which current circulates (most often it is 4-20 mA). The 24V power supply is a voltage source. The current value changes the sensor depending on the parameter. And the analog input acts as a receiver
industrial controller. From the above it is seen that the functioning of the remaining components of the system depends on its quality and reliable operation.
Circuit implementation
The composition of any such device includes the following modules:
- The insert is fusible.
- A step-down transformer.
- Diode bridge.
- Filter.
- Control block.
The fuse box is a fuse that protects the device from overload. As soon as a high current value is applied to the input, it burns out, as a result of which the entire system is de-energized. At the same time, all its components remain operational. The transformer consists of two windings. The first of them is primary (220V is supplied to it), and the other is secondary, on which 24V is obtained. That is, it just only lowers the voltage. The diode bridge from a variable signal makes a constant. The filter stabilizes all output parameters by smoothing out various ripples. The last component - the control unit - can only be found in modern devices such as a 24V power supply. He measures
output signals. If they go beyond the permissible limits, de-energizes the current loop. However, this situation persists until their value returns to normal.
Specifications
- Maximum output current.
- Power source power.
- The number of output channels.
- Degree of protection of the case.
- Type of mount.
- Operating temperature range.
The first two parameters are interconnected. For example, if the maximum current of 22 mA is allowed at the output, then the power of the unit will be 5.28 W (22 mA multiplied by 24 V, current by voltage). To minimize the space occupied by such devices in measuring cabinets, multichannel sources are used. This is justified in cases where there are many measuring parameters in the system. The degree of protection of the housing is indicated by the letters "IP" and a digital index. The larger it is, the more reliable everything inside is protected. This value needs to be paid attention to when exploitation is required in an aggressive environment (for example, in the chemical or metallurgical industry). According to the type of fastening, such devices are of two types: screw and DIN rail. The first of these are obsolete modifications that are gradually moving out of use. The latter are installed on a special rail, and today it has become the de facto standard. The last parameter that characterizes the power supply
24V is a range of operating temperatures. It is worth paying attention only if it is planned to operate in some extreme conditions (for example, when the value of this parameter can drop to minus 40-50 degrees Celsius).
How to choose?
The algorithm for selecting such devices is as follows. We determine the number of consumers and their total capacity. Suppose, it is supposed to work with a powerful solenoid valve at 100W and current at a peak load of 5A. It is recommended to take a power reserve of about 20%. To do this, we multiply 100W by 1.2, we get 120W - the power indicating that our 24V 5A power supply (120W / 24V) will have just such indicators. It is from devices with such characteristics that you need to choose. Further, it is necessary to take into account operating conditions and temperature conditions, if necessary.
To summarize
24V power supplies are very important components of modern process control systems. Without them, it is impossible to imagine the full-fledged operation of any measuring system today. Their choice must be approached very thoroughly. In case of failure of such a component, failure of other parts of the system is possible.