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渣漿泵測量儀表的使用方法
測量儀表是泵測試中獲得測試數(shù)據(jù)的設(shè)備，它將直接影響整個(gè)測試數(shù)據(jù)值的正確、真實(shí)、可信。測量儀表的選擇原則是:要符合國家有關(guān)計(jì)量的標(biāo)準(zhǔn)和要求，要達(dá)到試驗(yàn)精度的要求。泵的測量儀表包括:流量測量儀表;壓力或壓差測量儀表;轉(zhuǎn)速測量儀表;功率(轉(zhuǎn)矩)測量儀表及噪聲、振動(dòng)、溫升等測量儀表。
一、流量測量儀表或方法
流量測量儀表或方法可分為實(shí)驗(yàn)室的測量儀表和現(xiàn)場測量儀表兩類。
實(shí)驗(yàn)室的測量儀表和方法有:
(1)原始方法:稱重法、容積法;
(2)差壓裝置(成稱節(jié)流裝置):標(biāo)準(zhǔn)孔板、標(biāo)準(zhǔn)噴嘴、經(jīng)典文丘里管；
(3)水堰。
(4)電磁流量計(jì)。
(5)渦輪流量計(jì)。
現(xiàn)場測量儀表和方法有:
(1)超聲波流量計(jì)。
(2)速度面積法。
(3)稀釋法。
1. 稱重法、容積法
(1)測量原理:是在一 定時(shí)間內(nèi)，由一個(gè)容器收集排出的流體，然后用稱重法得到流體的重量或用量桶測得流體的體積除以時(shí)間，便得到其流量值。
(2)測量方法:稱重法如圖8-13所示。稱重容器的容量要足夠大，注水時(shí)間應(yīng)不小于30s，衡器(稱)的精度要求高于0.01%， 如果為容器法，即將稱重容器和衡器換成量筒便是。
換向器用來向容器注水的切換裝置，換向器的工作應(yīng)足夠快(應(yīng)小于0.1s)，以減少測量誤差。
時(shí)間測量與控制系統(tǒng)的分辨率應(yīng)小于0.1s，并要與換向器同步。
(3)流量計(jì)算：
1.稱重法：
②容積法:
(4)稱重法、容積法的特點(diǎn):
①稱重法、容積法雖為最原始的測量方法，但其測量精確度很高，一般可達(dá)0. 1%一0.3%，所以常被用來校準(zhǔn)其他形式的流量計(jì)。
②測量較繁復(fù)，測量時(shí)間長，不能測量瞬時(shí)流量，只能用來測量平均流量。
2.差壓裝置(節(jié)流裝置或節(jié)流裝置流量計(jì))
(1)測量原理:如圖8-14所示，充滿管道內(nèi)的流體流經(jīng)管道內(nèi)的節(jié)流裝置時(shí)，流束將在此形成局部收縮，從而使流速增加，靜壓力降低，于是在節(jié)流裝置前后產(chǎn)生了壓差，流量越大，壓差越大，通過測量節(jié)流裝置前后的壓差，就可以計(jì)算出流體流量的大小。
(2)差壓裝置組成:
①節(jié)流件:它是差壓裝置中造成流體收縮而使其上、下游兩側(cè)產(chǎn)生差壓的元件。節(jié)流件有:標(biāo)準(zhǔn)孔板、標(biāo)準(zhǔn)噴嘴、長徑噴嘴、經(jīng)典文丘里管、文丘里噴嘴、錐形入口孔板、1/4圓孔板、偏心孔板，圓缺孔板等。常用的節(jié)流件是標(biāo)準(zhǔn)孔板、標(biāo)準(zhǔn)噴嘴和經(jīng)典文丘里管。
?取壓方式和裝置:取壓是提取節(jié)流件上、下游兩側(cè)產(chǎn)生的差壓值，它有角接取壓方式、法蘭取壓方式、D-d/2 取壓方式。差壓的測定可用液柱式差壓計(jì)或差壓傳感器來測量。連接導(dǎo)壓管內(nèi)必須完全充滿液體，排盡空氣。
③節(jié)流件前后穩(wěn)流直管段:節(jié)流件前后穩(wěn)流直管段的長度L1、L2 必須足夠長，以便保證流經(jīng)圖8- 14 節(jié)流裝置流量測量原理圖 節(jié)流件時(shí)流速均勻，L1、I2 的長度與節(jié)流件的直徑比β=d/D,節(jié)流件型式及安裝等有關(guān)。具體尺寸可參閱有關(guān)資求得(鄭夢海:泵測試實(shí)用技術(shù)或流量測量節(jié)流裝置)。
(3)流量計(jì)算方法:
當(dāng)節(jié)流裝置和被測波體確定后，Q、8、d、ρ都為定值，可以總括為系數(shù)k，則
如果差壓測量用水銀差壓計(jì)Ap =yh，y已確定，歸納到流量計(jì)流量系數(shù)中去，流量計(jì)流量系數(shù)為k，則
所以，平時(shí)使用時(shí)，常將h或k事先計(jì)算出，只要測得差壓值Ap或水銀差壓計(jì)讀數(shù)h代人到式(8-16)或式(8-17) 中去計(jì)算就很方便。為精確起見，可以用重量法或容積法標(biāo)定出k或k'值。
(4)差壓裝置流量測量的特點(diǎn):
①差壓裝置流量測量可有較高的精度，并可不經(jīng)標(biāo)定使用，精度可達(dá)土1.0%-土1. 5%，如經(jīng)標(biāo)定，可達(dá)+0.35%一+0.5%， 如用原位標(biāo)定可達(dá)+0.1%~ +:0.3%，并且在使用中可不需要按標(biāo)定周期進(jìn)行標(biāo)定;
②操作方便，測量快，可測得瞬時(shí)流量;
③結(jié)構(gòu)簡單，制造方便(可自行制造)，使用可能，價(jià)格便宜:
④節(jié)流件前后要求的的直管段要求較長，試驗(yàn)室面積大;
⑤流量測量范田小，一般為1:3；
⑥用力損失大，不適宜低揚(yáng)程泵的流進(jìn)測量。
3. 堰
(1) 工作原理 渣漿泵廠家
如圖8-15所示，堰的流量測量的工作原理是基于水力學(xué)孔口出流，當(dāng)液體流經(jīng)“堰口”時(shí)受阻，液面在堰口前升高，液體經(jīng)堰口頂部溢出，堰的水頭h越高，溢出的流量就越大，所以通過測量堰的水頭高h,就可以計(jì)算出流量的大小。
堰按其堰口的形狀可分為直角三角堰、矩形堰和全寬堰，如圖8 - 16所示。三角堰適用于較小流量的測量，矩形堰用于較大流量的測量，全寬堰用于大流量的測量。
(2)流量計(jì)算公式
①直角三角堰:
Usage of measuring instrument for slurry pump
The measuring instrument is the equipment which obtains the test data in the pump test, it will directly affect the correctness, authenticity and credibility of the whole test data value. The selection principle of measuring instruments is: to meet the national standards and requirements of measurement, to meet the requirements of test accuracy. The measuring instruments of the pump include: flow measuring instruments; pressure or differential pressure measuring instruments; speed measuring instruments; power (torque) measuring instruments and noise, vibration, temperature rise and other measuring instruments.
I. flow measuring instrument or method
The flow measuring instruments or methods can be divided into laboratory measuring instruments and field measuring instruments.
The measuring instruments and methods in the laboratory are as follows:
(1) original methods: weighing method and volume method;
(2) differential pressure device (called throttling device): standard orifice, standard nozzle, classic venturi;
(3) weir.
(4) electromagnetic flowmeter.
(5) turbine flowmeter.
The field measuring instruments and methods are as follows:
(1) ultrasonic flowmeter.
(2) velocity area method.
(3) dilution method.
1. Weighing method and volume method
(1) measurement principle: it is to collect the discharged fluid from a container within a certain period of time, and then use the weighing method to get the weight of the fluid or the volume of the fluid measured in the measuring barrel divided by the time to get the flow value.
(2) measurement method: the weighing method is shown in Figure 8-13. The capacity of the weighing container shall be large enough, the water injection time shall not be less than 30s, and the accuracy of the scale (scale) shall be higher than 0.01%. If it is the container method, it is necessary to replace the weighing container and scale with the measuring cylinder.
The diverter is a switching device used to inject water into the vessel. The operation of the diverter shall be fast enough (less than 0.1s) to reduce the measurement error.
The resolution of time measurement and control system shall be less than 0.1s, and shall be synchronized with commutator.
(3) flow calculation:
1. Weighing method:
② volume method:
(4) characteristics of weighing method and volume method:
① although weighing method and volume method are the most original measurement methods, their measurement accuracy is very high, generally up to 0.1% - 0.3%, so they are often used to calibrate other forms of flowmeter.
② the measurement is complex and time-consuming, so it can't measure the instantaneous flow, but can only be used to measure the average flow.
2. Differential pressure device (throttling device or throttling device flowmeter)
(1) measurement principle: as shown in Figure 8-14, when the fluid in the full pipeline flows through the throttling device in the pipeline, the flow beam will form a local contraction here, so that the flow rate will increase and the static pressure will decrease, so there will be a pressure difference before and after the throttling device. The larger the flow rate is, the greater the pressure difference is. By measuring the pressure difference before and after the throttling device, the size of the fluid flow can be calculated.
(2) composition of differential pressure device:
① throttling element: it is the element in the differential pressure device that causes fluid contraction and causes differential pressure on both sides of its upstream and downstream. Throttling parts include: standard orifice, standard nozzle, long diameter nozzle, classic venturi tube, venturi nozzle, cone-shaped inlet orifice, 1 / 4 round orifice, eccentric orifice, round lack orifice, etc. The common throttling parts are standard orifice, standard nozzle and classic venturi.
? pressure taking mode and device: pressure taking is to extract the differential pressure value generated at the upstream and downstream sides of the throttling part. It has angle connection pressure taking mode, flange pressure taking mode and D-D / 2 pressure taking mode. Differential pressure can be measured by liquid column differential pressure gauge or differential pressure sensor. The connecting impulse pipe must be completely filled with liquid and drained of air.
③ steady flow straight pipe section before and after throttling piece: the length L1 and L2 of the steady flow straight pipe section before and after throttling piece must be long enough to ensure the flow velocity is uniform when flowing through throttling piece in Fig. 8-14 throttling device flow measurement schematic diagram. The length of L1 and I2 is related to the diameter ratio β = D / D of throttling piece, the type and installation of throttling piece, etc. Please refer to relevant information for specific dimensions (Zheng Menghai: practical technology of pump test or flow measurement throttling device).
(3) flow calculation method:
When the throttling device and the measured wave body are determined, Q, 8, D and ρ are all fixed values, which can be summed up as the coefficient K, then
If the mercury differential pressure gauge AP = YH, y has been determined for differential pressure measurement, and it is summed up in the flow coefficient of the flowmeter, and the flow coefficient of the flowmeter is k, then
Therefore, in normal use, h or K is usually calculated in advance, so long as the measured differential pressure value AP or mercury differential pressure meter reading h is replaced by formula (8-16) or formula (8-17) for calculation, it is very convenient. For accuracy, K or K 'value can be calibrated by weight method or volume method.
(4) characteristics of flow measurement of differential pressure device:
① the flow measurement of differential pressure device can have high accuracy and can be used without calibration. The accuracy can be as high as 1.0% - 1.5%. If calibrated, it can be as high as + 0.35% - 0.5%. If calibrated in situ, it can be as high as + 0.1% ~ +: 0.3%. And in use, it is unnecessary to calibrate according to calibration cycle;
② convenient operation, fast measurement and instantaneous flow measurement;
③ simple structure, convenient manufacturing (self manufacturing), possible use and low price:
④ the straight pipe section required before and after the throttling parts is long, and the area of the test room is large;
⑤ flow measurement fan Tian is small, generally 1:3;
⑥ the force loss is large, which is not suitable for the flow measurement of low head pump.
3. weir
(1) working principle: slurry pump manufacturer
As shown in Figure 8-15, the flow measurement principle of weir is based on the outlet of hydraulic orifice. When the liquid flows through the "weir mouth", the liquid level rises in front of the weir mouth, and the liquid overflows through the top of the weir mouth. The higher the head h of the weir, the greater the overflow flow. Therefore, the flow can be calculated by measuring the head h of the weir.
According to the shape of the weir mouth, the weir can be divided into right triangle weir, rectangular weir and full width weir, as shown in Figure 8-16. Triangle weir is suitable for the measurement of small flow, rectangle weir for the measurement of large flow and full width weir for the measurement of large flow.
(2) flow calculation formula
(1)
