The obstruction or leakage of the cooling water of the stator bar of a turbine-generator will lead to a failure. So it is indispensable to take the flow rate test during the manufacturer or the overhaul of a generator. But there is no flow instrument available be applicable to the situation and it is in dire need of an instrument that can be used to detect the flow rate of cooling water of the stator bar of turbine-generator. According to the condition of the power plant, we adopt the ultrasonic flow-detecting technique and develop the ultrasonic flowmeter to test the flow rate of the cooling water of the turbine-generator. The flowmeter can not only be used to measure the flow rate in power plants, but also be used in the generator's leaving factory transaction.
Because the small diameter and low flow rates of the turbine generator cooling water, the differences in transit time are extremely small and even modern high-speed electronics can not deal easily. As a result, the conventional ultrasonic transit-time technique can not be exploited directly here. Therefore an ultrasonic sing-around method is introduced and which can cumulate the small time intervals and handle the problem successfully. In this paper the flowmeter is designed using the ultrasonic sing-around method and transit-time technique. The scheme of the flowmeter is also presented.
The design of the electronic circuit is a central part of the development of the flowmeter. The ultrasonic emissive circuit is crucial and will affect the system profoundly. This apparatus need an emissive circuit with high repeating frequency. But the general emission circuits can not transmit rapidly because they use the silicon controlled rectifer (SCR). The circuit can emit with high recurrence rate when we adopt the late-model metallic oxide semiconductor field effect transistor (MOSFET) as the control element of the emission circuit and the circuit can emit with high repeat frequency. The receive-amplifier unit with a wide frequency bandwidth and adjustable amplification is also design and which is fit for the apparatus.
To intelligentize the flowmeter, a single chip microcomputer is employed. The microcomputer can control the time sequence of the measuring unit. Then it read the data from the counter then processes them and sends them to the upper computer in the end. The accessory of the control circuit and various hardware anti-interference methods are also designed.
Software of the single chip microcomputer and upper computer are devised, too. Various software antijamming methods are put in practice. After taking the measures, the flowmeter can work with well-pleasing stabilization. In the experiment, the flowmeter works with a high repeat accuracy and the result is satisfying. It proved that the ultrasonic flowmeter will be able to detect the flow rates of cooling water of the stator bar of turbine-generators.
