ASHRAE FUNDAMENTALS SI CH 37-2017 Measurement and Instruments.pdf
《ASHRAE FUNDAMENTALS SI CH 37-2017 Measurement and Instruments.pdf》由会员分享,可在线阅读,更多相关《ASHRAE FUNDAMENTALS SI CH 37-2017 Measurement and Instruments.pdf(40页珍藏版)》请在麦多课文档分享上搜索。
1、37.1CHAPTER 37MEASUREMENT AND INSTRUMENTSTerminology . 37.1Uncertainty Analysis 37.3Temperature Measurement 37.4Humidity Measurement 37.10Pressure Measurement. 37.13Air Velocity Measurement 37.14Flow Rate Measurement 37.20Air Infiltration, Airtightness, and Outdoor Air Ventilation Rate Measurement.
2、37.24Carbon Dioxide Measurement. 37.25Electric Measurement 37.27Rotative Speed and Position Measurement 37.28Sound and Vibration Measurement 37.29Lighting Measurement . 37.31Thermal Comfort Measurement . 37.31Moisture Content and Transfer Measurement 37.32Heat Transfer Through Building Materials . 3
3、7.34Air Contaminant Measurement 37.35Combustion Analysis 37.35Data Acquisition and Recording 37.35Mechanical Power Measurement. 37.37VAC engineers and technicians require instruments for bothH laboratory work and fieldwork. Precision is more essential inthe laboratory, where research and development
4、 are undertaken, thanin the field, where acceptance and adjustment tests are conducted.This chapter describes the characteristics and uses of some of theseinstruments.1. TERMINOLOGYThe following definitions are generally accepted.Accuracy. Ability of an instrument to indicate the true value ofmeasur
5、ed quantity. This is often confused with inaccuracy, which isthe departure from the true value to which all causes of error (e.g.,hysteresis, nonlinearity, drift, temperature effect) contribute.Amplitude. Magnitude of variation from its equilibrium or aver-age value in an alternating quantity.Averag
6、e. Sum of a number of values divided by the number ofvalues.Bandwidth. Range of frequencies over which a given device isdesigned to operate within specified limits.Bias. Tendency of an estimate to deviate in one direction from atrue value (a systematic error).Calibration. (1) Process of comparing a
7、set of discrete magni-tudes or the characteristic curve of a continuously varying magni-tude with another set or curve previously established as a standard.Deviation between indicated values and their corresponding stan-dard values constitutes the correction (or calibration curve) for infer-ring tru
8、e magnitude from indicated magnitude thereafter; (2) processof adjusting an instrument to fix, reduce, or eliminate the deviationdefined in (1). Calibration reduces bias (systematic) errors.Calibration curve. (1) Path or locus of a point that moves so thatits graphed coordinates correspond to values
9、 of input signals andoutput deflections; (2) plot of error versus input (or output).Confidence. Degree to which a statement (measurement) isbelieved to be true.Dead band. Range of values of the measured variable to whichan instrument will not effectively respond. The effect of dead band issimilar to
10、 hysteresis, as shown in Figure 1.Deviate. Any item of a statistical distribution that differs from theselected measure of control tendency (average, median, mode).Deviation. Difference between a single measured value and themean (average) value of a population or sample.Diameter, equivalent. The di
11、ameter of a circle having the samearea as the rectangular flow channel cross section.Deviation, standard. Square root of the average of the squares ofthe deviations from the mean (root mean square deviation). A mea-sure of dispersion of a population.Distortion. Unwanted change in wave form. Principa
12、l forms ofdistortion are inherent nonlinearity of the device, nonuniformresponse at different frequencies, and lack of constant proportional-ity between phase-shift and frequency. (A wanted or intentionalchange might be identical, but it is called modulation.)Drift. Gradual, undesired change in outp
13、ut over a period of timethat is unrelated to input, environment, or load. Drift is gradual; ifvariation is rapid and recurrent, with elements of both increasing anddecreasing output, the fluctuation is referred to as cycling.Dynamic error band. Spread or band of output-amplitude devi-ation incurred
14、by a constant-amplitude sine wave as its frequency isvaried over a specified portion of the frequency spectrum (see Staticerror band).Emissivity. Ratio of the amount of radiation emitted by a real sur-face to that of an ideal (blackbody) emitter at the same temperature.Error. Difference between the
15、true or actual value to be measured(input signal) and the indicated value (output) from the measuringsystem. Errors can be systematic or random.Error, accuracy. See Error, systematic.Error, fixed. See Error, systematic.Error, instrument. Error of an instruments measured value thatincludes random or
16、systematic errors.Error, precision. See Error, random.Error, probable. Error with a 50% or higher chance of occur-rence. A statement of probable error is of little value.Error, random. Statistical error caused by chance and not recur-ring. This term is a general category for errors that can take val
17、ues oneither side of an average value. To describe a random error, its dis-tribution must be known.Error, root mean square (RMS). Accuracy statement of a sys-tem comprising several items. For example, a laboratory potentiom-eter, volt box, null detector, and reference voltage source haveindividual a
18、ccuracy statements assigned to them. These errors aregenerally independent of one another, so a system of these units dis-plays an accuracy given by the square root of the sum of the squaresof the individual limits of error. For example, four individual errorsof 0.1% could yield a calibrated error o
19、f 0.4% but an RMS error ofonly 0.2%.Error, systematic. Persistent error not caused by chance; system-atic errors are causal. It is likely to have the same magnitude and signfor every instrument constructed with the same components andThe preparation of this chapter is assigned to TC 1.2, Instruments
20、 andMeasurements.37.2 2017 ASHRAE HandbookFundamentals (SI)procedures. Errors in calibrating equipment cause systematic errorsbecause all instruments calibrated are biased in the direction of thecalibrating equipment error. Voltage and resistance drifts over timeare generally in one direction and ar
21、e classed as systematic errors.Frequency response (flat). Portion of the frequency spectrumover which the measuring system has a constant value of amplituderesponse and a constant value of time lag. Input signals that havefrequency components within this range are indicated by the mea-suring system
22、(without distortion).Hydraulic diameter Dh. Defined as 4Ac/Pwet, where Acis flowcross-sectional area and Pwetis the wetted perimeter (perimeter incontact with the flowing fluid). For a rectangular duct with dimen-sions W H, the hydraulic diameter is Dh= 2HW/(H + W ). Therelated quantity effective or
23、 equivalent diameter is defined as thediameter of a circular tube having the same cross-sectional area asthe actual flow channel. For a rectangular flow channel, the effectivediameter is Deff= .Hysteresis. Summation of all effects, under constant environ-mental conditions, that cause an instruments
24、output to assumedifferent values at a given stimulus point when that point is ap-proached with increasing or decreasing stimulus. Hysteresis in-cludes backlash. It is usually measured as a percent of full scalewhen input varies over the full increasing and decreasing range. Ininstrumentation, hyster
- 1.请仔细阅读文档,确保文档完整性,对于不预览、不比对内容而直接下载带来的问题本站不予受理。
- 2.下载的文档,不会出现我们的网址水印。
- 3、该文档所得收入(下载+内容+预览)归上传者、原创作者;如果您是本文档原作者,请点此认领!既往收益都归您。
本资源只提供5页预览,全部文档请下载后查看!喜欢就下载吧,查找使用更方便
10000 积分 0人已下载
下载 | 加入VIP,交流精品资源 |
- 配套讲稿:
如PPT文件的首页显示word图标,表示该PPT已包含配套word讲稿。双击word图标可打开word文档。
- 特殊限制:
部分文档作品中含有的国旗、国徽等图片,仅作为作品整体效果示例展示,禁止商用。设计者仅对作品中独创性部分享有著作权。
- 关 键 词:
- ASHRAEFUNDAMENTALSSICH372017MEASUREMENTANDINSTRUMENTSPDF

链接地址:http://www.mydoc123.com/p-454838.html