Solution of the problems in constant pressure water supply system of AC70

Fault Name:

Analysis of problems occurring in constant pressure water supply system of AC70 frequency inverter

Fault Symptom:

AC70 frequency inverter does not sleep on the constant pressure water supply system, the water pressure is too high, the pressure fluctuates and other issues.

Causes:

These problems of constant pressure water supply can be explained as abnormal parameter debugging, improper connection of pressure gauges, and damage to pressure gauges.

Solutions:

First I am going to explain our AC70 series frequency inverters are used in constant water supply that is controlled by the remote pressure gauge (the pressure gauge is technically similar to pressure transmitter), and the parameters that need to be adjusted are E1-01 (external start), E-02=9 (constant water supply PID), H-13=0 (analog VS1 feedback), H-16=demanded pressure value/the maximum pressure*100%, H-18=the maximum pressure value of the remote pressure gauge and not the standard 100%, H-24 starting threshold, H-25 dormant threshold, E-11 the lowest frequency, monitoring parameters C-07 PID setting value, C-08 PID feedback value. Even changes don’t change the essence.

Analysis:

The frequency inverter has been running at 50Hz and cannot stop

Check the value of C-08; see if it’s smaller than that of C-07:

1) If the value of C-08 is smaller than that of C-07, it means the feedback value is a little bit small that causes that the frequency inverter inspects the pressure hasn’t reached the setting value, so we need to increase the H-17 feedback according to the actual pressure value of the pressure gauge and let the value of C-08 be equivalent to that of the pressure gauge.

2) If the value of C-08 is 0.0 and the actual pressure has already been high, so it may causes by two reasons: wrong wirings lead that the frequency inverter cannot accept the analog from 0 to 10V; the pressure is damaged so you could replace them and finish it again.
The water pressure is too high and the set pressure has been exceeded, and the frequency inverter is still running. This case is similar to the case in which the frequency inverter are running at 50HZ that was just analyzed cannot be stopped. The analysis and processing are the same.

No dormancy:

3. This issue is the most difficult to deal with because of the weakness of our 70 software, after the actual pressure reaches the set pressure, it must be ensured that the pressure does not change within 60 seconds, if the pressure changes slightly, and the frequency inverter starts immediately to fill the pressure. Pipeline leaking or check valve sealing effect is not good at the scene; the frequency inverter is difficult to get dormant, at this time, you can explain to the customer that the pipeline is being processed, or try to reduce the dormant pressure threshold.

High pressure fluctuations or unresponsive pressure:

The two phenomena are completely opposite. One of them is that the PID response is slow, resulting in insufficient pressure supply, and the other one is that the PID response is sensitive, resulting in a large swing of the pointer of the gauge. The adjustable parameter of the frequency inverter is the same, but it is the opposite of the tuning. H-19 P value, H-20 I value, H-22 sampling period, H-21 D value, generally, there is no need to adjust the D value. When the P value gain is large, the response is fast, but if the P value is too large, the oscillation will occur. When the gain is small, the response is delayed. When I value integration time is large, the response is sluggish, and in addition, the ability to control the external disturbance becomes worse; when the integration time is small, the response speed is fast. If it is too small, oscillations will occur too.