The physical quantity directly measured by the ultrasonic open channel flowmeter is the liquid level. For the open channel flow measurement, install the water sump on the open channel. The measuring water trough converts the flow rate in the open channel into the level of the liquid level. The physical quantity directly measured by the ultrasonic open channel flowmeter is the liquid level. For the open channel flow measurement, install the water sump on the open channel. The measuring water trough converts the flow rate in the open channel into the level of the liquid level. The water level in the water tank is measured, and the flow rate is calculated according to the water level flow relationship of the corresponding water tank. The correspondence between the flow rate and the water level in the common open channel is affected by the slope ratio and surface roughness of the channel. The installation of the water gutter in the channel produces a throttling effect, so that the flow in the open channel has a fixed correspondence with the liquid level. This correspondence depends mainly on the structural size of the water gutter and the influence of the channel is minimized.
When the open channel flowmeter is working, the ultrasonic sensor is fixedly mounted above the measured liquid level. The probe emits a pulsed ultrasonic wave to the surface of the water. The sound wave reaches the liquid surface through the air, and the sound wave is reflected by the liquid surface into a reflected wave, and the probe receives the reflected wave as an echo. The correction rod below the probe also produces a reflection that is received by the probe called a correction wave. The open channel flowmeter determines the distance from the probe to the liquid surface based on the time difference between the transmitted wave and the echo, the transmitted wave and the corrected wave. The liquid level height H is obtained by subtracting the distance L from the probe to the zero level of the water level. as the picture shows.
The probe of the open channel flowmeter is installed at the position of the water level observation point of the measuring water channel, and the water level flowing through the water level groove is measured. When the open channel flowmeter is installed, the water level flow relationship of the corresponding water level groove is loaded into the instrument internal memory via the button in the form of a number table. The microprocessor of the open channel flowmeter uses the measured water level to find the corresponding flow value by using the look-up table method. The number between two adjacent values ​​in the table is obtained by linear interpolation.
The selection of ultrasonic open channel flowmeters is a factor:
1. Waterway size and shape, flow rate range, maximum flow rate and minimum flow rate; 2. Measurement accuracy requirements; 3. Flowmeter setting place and environmental conditions; 4. Liquid condition, cleanliness, solid phase concentration, corrosiveness; The allowable drop (or elevated water level) and channel slope on site; 6. Instrument parts and materials in contact with liquid; 7. Ultrasonic flow meter and electromagnetic flow rate timing should be investigated separately for liquid turbidity or conductivity. Refer to the ultrasonic flowmeter and electromagnetic flowmeter requirements.
Estimate channel traffic and raise water levels:
For new units, the channel flow and the proposed installation location can be calculated through the process flow, and then the meter specifications are selected. For the old enterprise to add meters, it is necessary to estimate the existing channel flow and confirm that the upstream water level of the instrument is allowed to rise; that is, to determine the flow meter specification and flow range, depending on the channel peak flow and the allowable increase of the water level. Usually there is a float method and Two methods of estimating daily emissions.
1) The float method can be used to measure and estimate the flow rate using the floating float method. When the maximum flow rate is selected, the distance between the two persons is L (20~50m) standing beside the straight channel, and the upstream one is placed on the float (usually a wooden disc), and the downstream one starts the timing when the wood chip is placed, and stops when the float arrives. Timing, time t, find the channel surface velocity Ï… m / s (Ï… = L / t). After measuring the channel cross-sectional area Am2, the K--------- correction coefficient of the flow rate Q can be estimated from the equation (5). Since the surface velocity is greater than the average flow velocity, it is generally 0.84~0.90.
2) Estimating the peak flow Qp from the daily discharge Qd. In the case of no-floating method or new system, the actual (or designed) emission can be used to estimate the peak flow. The formula is given by equation (6) or (7). Ku------ uneven coefficient, if it is uniform continuous discharge, it can take 1.1~1.2; H ------- cumulative hours of concentrated discharge per day, if it is uneven continuous discharge, it is calculated according to the concentrated discharge hour .
(2) Determine the elevated water level
Except for the flow rate-water level flowmeter and the non-full-tube electromagnetic flowmeter, the upstream of the channel must be raised to a higher water level. For the newly designed canal system, the elevated water level can be determined by considering the measurement flow range and surrounding environmental conditions. For the existing channels, when selecting the flowmeter, consider the influence of the upstream canal water level rise (such as whether the water level will overflow the channel), and then select the instrument specifications according to the determined water level rise height and peak flow value.
Basic requirements for annual inspection and calibration The basic requirements for calibration should be as follows:
1) If the environmental conditions are calibrated in the calibration (calibration) room, the environmental conditions should meet the temperature and humidity requirements of the laboratory. If the calibration is carried out on site, the environmental conditions shall be subject to the conditions for the on-site use of the instrument.
2) As the standard instrument used for calibration, the error limit should be 1/3~1/10 of the error limit of the calibration.
3) Although the personnel calibration is different from the verification, the personnel who perform the calibration should also be effectively evaluated and obtain the corresponding certificate of conformity. Only the certificate holder will issue a calibration certificate and a calibration report, and only such certificates and reports will be considered. It's effective. This article is transferred from: electromagnetic flowmeter http://, orifice flowmeter http://
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