The working principle of the impeller type flowmeter is that the impeller is placed in the fluid to be measured, and is rotated by the impact of the fluid flow, and the flow rate is reflected by the speed of the impeller rotation. Typical impeller flow meters are water meters and turbine flow meters, which may be of mechanical transmission output or electrical pulse output. Generally, the water meter output of the mechanical transmission has low accuracy and the error is about ±2%, but the structure is simple and the cost is low. The domestic production has been mass-produced, standardized, generalized and serialized. The accuracy of the turbine flowmeter for electrical pulse signal output is high, with a typical error of ±0.2% to 0.5%.
Differential pressure flowmeter (variable pressure drop flowmeter)
The differential pressure flowmeter consists of a primary device and a secondary device. The primary device is called a flow measuring element and is installed in the pipe of the fluid to be measured, generating a pressure difference proportional to the flow rate (flow rate) for the secondary device to display the flow rate. The secondary device is called a display instrument. It receives the differential pressure signal generated by the measuring component and converts it to the corresponding flow for display. The primary device of the differential pressure flow meter is often a throttling device or a dynamic pressure measuring device (piteron, constant velocity tube, etc.). The secondary device is equipped with various mechanical, electronic and combined differential pressure gauges with flow display instruments. The differential pressure sensitive components of the differential pressure gauge are mostly elastic components. Since the differential pressure and the flow rate are in a square root relationship, the flow display instrument is equipped with an open square device to linearize the flow scale. Most meters also have a flow accumulator to display cumulative flow for economic accounting. This method of measuring flow using differential pressure has a long history and is relatively mature. Generally, countries all over the world use it in more important occasions, accounting for about 70% of various flow measurement methods. The flow measurement of the main steam, feed water, condensate, etc. of the power plant is based on this meter.
Fourth, the liquid turbine flowmeter put into operation the opening and closing sequence
1. The sequence of opening and closing of the operation
For flow sensors without a bypass line, first open the flow sensor upstream valve at a medium opening and then slowly open the downstream valve. Run at a small flow rate for a period of time (eg 10 minutes), then fully open the upstream valve, then open the large downstream valve opening to adjust to the required normal flow.
The flow sensor equipped with the bypass pipe first opens the bypass pipe valve to open the upstream valve at a medium opening degree, slowly opens the downstream valve, and closes the opening of the small bypass valve to make the instrument run for a period of time with a small flow rate. Then fully open the upstream valve, fully close the bypass valve (to ensure no leakage), and finally adjust the downstream valve opening to the required flow.
2. Activation of low temperature and high temperature fluids
The low-temperature fluid pipeline should drain the water in the pipeline before the flow, and then run for 15 minutes at a small flow rate, and then gradually increase to the normal flow. Slow down when stopping, so that the pipe temperature and ambient temperature are gradually approaching. High temperature fluid operation is similar to this.
Plug-in electromagnetic flowmeter features
Corrosion-resistant full stainless steel material, ABS full mold production probe structure is simple, firm, no moving parts, long service life, reliable measurement, strong anti-interference ability, small size, light weight, easy installation, small maintenance range, large measurement range, temperature-free measurement The influence of changes in density, pressure, viscosity, conductivity, etc., zero pressure loss can be installed and disassembled under continuous flow, which brings convenience to the user's maintenance. The manufacturing cost and installation cost are lower than the general electromagnetic flowmeter. It is especially suitable for large and medium-diameter pipeline flow measurement. It adopts advanced processing technology, solid-state packaging, vibration resistance and long life. It makes the meter have good measurement accuracy and stability. The flowmeter not only has 4-20mA current signal output, but also has 1-2000HZ frequency output digital communication output: RS485, RS232, HART, Modbus.