1) Shielded wires should be used for signal lines and control lines, which is good for preventing interference. When the line is longer, for example 100 m apart, the conductor cross-section should be enlarged. The signal line and control line should not be placed in the same cable trench or bridge as the power line, so as to avoid mutual interference. It is better to put the tube in place. This is more appropriate.
2) The signal is mainly transmitted using the current signal, because the current signal is not easily attenuated, and it is not susceptible to interference. In practice, the signal output by the sensor is a voltage signal, and the voltage signal can be converted into a current signal by the converter.
3) Inverter closed-loop control is generally positive, that is, the input signal is large, the output is also large (such as the central air-conditioning cooling and general pressure, flow, temperature and other control). But there are also counterproductive, that is, the input signal is large, and the output is inversely small (for example, when the central air conditioner is working in heating, and the heating heat pump for the heating station). Closed-loop control is shown in Figure 1.
4) When the pressure signal can be used in closed-loop control, do not use the flow signal. This is because the pressure signal sensor has a low price, is easy to install, has a small workload, and is easy to debug. However, if the process requires a flow rate ratio and requires precise, then a flow controller must be selected and a suitable flow meter (such as electromagnetic or target type) be selected based on the actual pressure, flow rate, temperature, medium, and speed. Vortex street, orifice plate, etc.).
5) The built-in PLC and PID functions of the inverter are suitable for systems with small signal variation and stable performance. However, because the built-in PLC and PID functions only adjust the time constant during operation, it is difficult to obtain satisfactory over-process requirements, and the debugging is time-consuming.
In addition, this adjustment is not intelligent, so it is not usually used, but the use of an external intelligent PID regulator. For example, the Fuji PXD series and Xiamen Anton are very convenient. When used, only set SV (upper limit value), PV (operation value) indication when working, and it is intelligent, ensure the best transition process conditions, and it is ideal to use. About PLC, according to the nature of the control quantity, the number of points, digital quantity, analog quantity, signal processing and other requirements, select various brands of external PLC, such as Siemens S7-400, S7-300, S7-200 and so on.
6) The signal converter is also often used in the peripheral circuit of the frequency converter. It is generally composed of a Hall element plus an electronic circuit. According to the signal transformation and processing methods, it can be divided into voltage change current, current change voltage, DC change AC, AC change DC, voltage change frequency, current change frequency, multiple input and output, multiple input and output, signal superposition, signal distribution, etc. Various converters. For example, the Santa Fe CE-T series isolated sensor/transmitter in Shenzhen is very convenient to use. Many domestic similar products, users can choose to use their own applications.
7) When the frequency converter is used, it is often necessary to allocate peripheral circuits. The methods are often:
(1) Logical functional circuits composed of self-made relays and other control elements;
(2) Buy off-the-shelf unit external circuits (for example, Mitsubishi Corporation of Japan);
(3) Select a simple programmable controller LOGO (foreign and domestic products);
(4) When using different functions of the inverter, use the function card (for example, Japan Sanken inverter);
(5) Selection of small and medium programmable controllers.
8) There are the following two kinds of common frequency conversion technological transformation plans for multiple pumps connected in parallel with constant pressure water supply (such as clear water pumps, medium and large-sized water pump stations, and central hot water supply stations in urban water plants).