Wednesday, March 27, 2019

Talk about HiPot Testing

Hipot Test is short name of high potential (high voltage) Test and it is also known as Dielectric Withstand Test. A hipot test checks for "good isolation and safety", not a function.



Hipot test makes surety of no current will flow from one point to another point.

Hipot test is the opposite of a continuity test, but an isolation test

Continuity Test checks surety of current flows easily from one point to another point while Hipot Test checks surety of current would not flow from one point to another point (and turn up the voltage really high just to make sure no current will flow).

Importance of HIPOT Testing

The hipot test is a nondestructive test that determines the adequacy of electrical insulation for the normally occurring over voltage transient. This is a high-voltage test that is applied to all devices for a specific time in order to ensure that the insulation is not marginal.

Hipot tests are helpful in finding nicked or crushed insulation, stray wire strands or braided shielding, conductive or corrosive contaminants around the conductors, terminal spacing problems, and tolerance errors in cables. Inadequate creepage and clearance distances introduced during the manufacturing process.

The production-line hipot test, however, is a test of the manufacturing process to determine whether the construction of a production unit is about the same as the construction of the unit that was subjected to type testing. Some of the process failures that can be detected by a production-line hipot test include, for example, a transformer wound in such a way that creepage and clearance have been reduced.

Such a failure could result from a new operator in the winding department.

HIPOT test is applied after tests such as fault condition, humidity, and vibration to determine whether any degradation has taken place.

Other examples include identifying a pinhole defect in insulation or finding an enlarged solder footprint.
As per IEC 60950, The Basic test Voltage for  Hipot test is the 2X (Operating Voltage) + 1000 V, such as in USA, normally set as 2X120+1000=1240VAC@60Hz. Note: different countries perhaps have the diffeeent standard. 
The reason for using 1000 V as part of the basic formula is that the insulation in any product can be subjected to normal day-to-day transient over voltages.

Experiments and research have shown that these over voltages can be as high as 1000 V.

Test method for HIPOT Test

Hipot testers usually connect one side of the supply to safety ground (Earth ground). The other side of the supply is connected to the conductor being tested. With the supply connected like this there are two places a given conductor can be connected: high voltage or ground.

When you have more than two contacts to be hipot tested you connect one contact to high voltage and connect all other contacts to ground. Testing a contact in this fashion makes sure it is isolated from all other contacts.

If the insulation between the two is adequate, then the application of a large voltage difference between the two conductors separated by the insulator would result in the flow of a very small current. Although this small current is acceptable, no breakdown of either the air insulation or the solid insulation should take place. Therefore, the current of interest is the current that is the result of a partial discharge or breakdown, rather than the current due to capacitive coupling.

Time Duration for HIPOT Test

The test duration must be in accordance with the safety standard being used. The test time for most standards, including products covered under IEC 60950, is 1 minute.

A typical rule of thumb is 110 to 120% of 2U + 1000 V for 1–2 seconds.

Current Setting for HIPOT Test

Most modern hipot testers allow the user to set the current limit. However, if the actual leakage current of the product is known, then the hipot test current can be predicted.

The best way to identify the trip level is to test some product samples and establish an average hipot current. Once this has been achieved, then the leakage current trip level should be set to a slightly higher value than the average figure.

Another method of establishing the current trip level would be to use the following mathematical formula:  E(Hipot) / E(Leakage) = I(Hipot) / 2XI(Leakage)

The hipot tester current trip level should be set high enough to avoid nuisance failure related to leakage current and, at the same time, low enough not to overlook a true breakdown in insulation.

Test Voltage for HIPOT Test

The majority of safety standards allow the use of either ac or dc voltage for a hipot test.

When using ac test voltage, the insulation in question is being stressed most when the voltage is at its peak, i.e., either at the positive or negative peak of the sine wave.

Therefore, if we use dc test voltage, we ensure that the dc test voltage is under root 2 (or 1.414) times the ac test voltage, so the value of the dc voltage is equal to the ac voltage peaks.

For example, for a 1500-V-ac voltage, the equivalent dc voltage to produce the same amount of stress on the insulation would be 1500 x 1.414 or 2121 V dc.

Advantages and Disadvantages of use DC Voltage for Hipot Test

One of the advantages of using a dc test voltage is that the leakage current trip can be set to a much lower value than that of an ac test voltage. This would allow a manufacturer to filter those products that have marginal insulation, which would have been passed by an ac tester.

When using a dc hipot tester, the capacitors in the circuit could be highly charged and, therefore, a safe-discharge device or setup is needed. However, it is a good practice to always ensure that a product is discharged, regardless of the test voltage or its nature, before it is handled.

It applies the voltage gradually. By monitoring the current flow as voltages increase, an operator can detect a potential insulation breakdown before it occurs. A minor disadvantage of the dc hipot tester is that because dc test voltages are more difficult to generate, the cost of a dc tester may be slightly higher than that of an ac tester.

The main advantage of the dc test is DC Voltage does not produce harmful discharge as readily occur in AC.

It can be applied at higher levels without risk or injuring good insulation. This higher potential can literally "sweep-out" far more local defects.

The simple series circuit path of a local defect is more easily carbonized or reduced in resistance by the dc leakage current than by ac, and the lower the fault path resistance becomes, the more the leakage current increased, thus producing a "snow balling" effect which leads to the small visible dielectric puncture usually observed. Since the dc is free of capacitive division, it is more effective in picking out mechanical damage as well as inclusions or areas in the dielectric which have lower resistance.

Advantages and Disadvantages of use AC Voltage for Hipot Test

One of the advantages of an ac hipot test is that it can check both voltage polarities, whereas a dc test charges the insulation in only one polarity. This may become a concern for products that actually use ac voltage for their normal operation. The test setup and procedures are identical for both ac and dc hipot tests.

A minor disadvantage of the ac hipot tester is that if the circuit under test has large values of Y capacitors, then, depending on the current trip setting of the hipot tester, the ac tester could indicate a failure. Most safety standards allow the user to disconnect the Y capacitors prior to testing or, alternatively, to use a dc hipot tester.

The dc hipot tester would not indicate the failure of a unit even with high Y capacitors because the Y capacitors see the voltage but don't pass any current.

Safety precautions during HIPOT Test

During a HIPOT Test, There may be at some risk so to minimize risk of injury from electrical shock make sure HIPOT equipment follows these guidelines:

  • The total charge you can receive in a shock should not exceed 45 uC.
  • The total hipot energy should not exceed 350 mJ.
  • The total current should not exceed 5 mA peak (3.5 mA rms)
  • The fault current should not stay on longer than 10 mS.
  • If the tester doesn't meet these requirements then make sure it has a safety interlock system that guarantees you cannot contact the cable while it is being hipot tested.
For Cable

  • Verify the correct operation of the safety circuits in the equipment every time you calibrate it.
  • Don't touch the cable during hipot testing.
  • Allow the hipot testing to complete before removing the cable.
  • Wear insulating gloves.
  • Don't allow children to use the equipment.
  • If you have any electronic implants then don't use the equipment.
-------------------
Orginal linkage here with a little bit modification and thanks, and iTestGroup also provide the HiPot testing solution for your product and safety, contact with iTestGroup via sales@itestgroup.com 

Saturday, March 23, 2019

Noise: 为什么电压端子悬空仪器显示仍有数值?

功率分析仪、功率计,万用表在测试电压时,有时会发现还没有接入测试电压,仪器就显示有一定的数值,其实这不是仪器故障,今天我们一起来揭秘。

    电磁感应原理

    大家是否还记得我们高中时学习的物理知识,电磁感应原理。相信很多人在学习电磁感应原理以及左右手定则的时候一定非常痛苦,我们先来回顾一下。电磁感应定律也叫法拉第电磁感应定律,电磁感应现象是指因磁通量变化产生感应电动势的现象,例如,闭合电路的一部分导体在磁场里做切割磁感线的运动时,导体中就会产生电流,产生的电流称为感应电流,产生的电动势(电压)称为感应电动势。所以导体在磁场中运动就会产生感应电流,形成感应电动势(电压),同理静止的导体在变化的磁场中也会产生感应电流形成感应电动势(电压),这就是电磁场变化的原理。


空气中的电磁环境

如今我们的生活中与电是万万分不开的,家用电器、电瓶车、电动车、广播、电机等等,因此空气中会存在着各种各样的电磁场,所有这些会对测量仪器造成影响的电磁场,我们称为电磁噪声。


        一般的电磁噪声对测试测量不会产生影响,各类电磁噪声频率范围不同,在空气中会不断衰减,所以通常可以忽略不计。但是因为电磁噪声的存在,对一些带宽、精度比较高的测试仪器就会造成影响。比如功率计和功率分析仪等产品,其精度高、带宽大,在小量程时如果操作不当,容易受电磁干扰影响造成误解。比如仪器电压端子悬空,量程设置较小时,仪器会显示一定的电压值,这个就是典型的受电磁噪声影响的结果。


如何避免噪声影响

首先我们要说明一个问题,电压通道输入为零的状态其实并不是开路状态,而是输入短路(用短线连接高低端子)状态。电压通道测量输入阻抗极高,开路状态下会拾取空间电磁噪声,就会出现电压测量值不为零的现象。所以如果我们发现仪器出现悬空时电压不为零,可以拿一根短线,把仪器电压端口的高低端短接,然后再查看数值是否为零,此时才是电压通道的零状态,显示也就为零了。除了短接之外,我们还有注意仪器的一些关键设置,比如PT比例是否设置正确,PT是否正常开关,电压量程是否合适,仪器供电接地是否良好,以保证最终测量准确进行。



(注:以下段落是周立功广告部分,既然转载ZLG文章,也不避讳地同时转载其软文广告了。)

ZLG立功科技・致远电子PA8000拥有丰富的触发方式,可以针对不同的场景进行触发,是一款认证级功率分析仪,功率精度高达0.01%、带宽高达5MHz,是逆变器、变频器与电源产品能效测量的基准,也是标准实验室认证检测的依据。



Saturday, June 2, 2018

How to Generate the PDF Report through LabVIEW

There has been a previous sister article (reply the key word "WORD" to get this sister article - editor's note: This article is reproduced from the WeChat public number "LabVIEW-Jobs", so you need to reply to the public number.) It's about how to read the contents of MS WORD documents through LabVIEW. At the end of the article, there is a primer that LabVIEW can also complete the production of MS WORD documents and PDF format documents. PDF is a very complex format, so here are some tools to achieve our goals. It's also from the story of a sister article, a PDF format report generated by a customer's production test software, which solved the read problem and thought how it was generated. After looking at every corner of the software, the key word "itextsharp©" seems to be related, finding the source through a search - itextsharp© is indeed an open source library that specializes in dealing with PDF. Those who are interested can learn more about this library.

 

Itextsharp© free open source library, the main tool of this article. It has served tens of thousands of people, and it is necessary to briefly introduce the source. At present, the open source library has been published on two major hosting platforms: https://github.com/itext/itextsharp and https://sourceforge.net/projects/itextsharp/, which are interested in going in and worshipping the big gods--the great people. The details are not introduced. Let me explain the copyright license of this tool. Itextsharp© is completely free, before the fourth edition is the open source MPL and LGPL protocol, the popular free freedom of open source, whether your own project is open source or closed source. After the 4.2 version, itextsharp© is still open source, but you must also open your own project, that is, the AGPL protocol. And commercial projects unwilling to open source must purchase copyrights, and names become iText© (Fifth Edition), no longer itextsharp. As you can see from the screenshot below, we use the 4.1.6.0 version, which should be without copyright.


 

Even if you get this open source library, further integration into LabVIEW® is very tedious, since there are a lot of parameters to be configured. So here we want to introduce another LabVIEW-based toolkit which called Exaprom PDF. This toolkit developed based on our previous itextsharp© by a Canadian company. Since itextsharp© is open source, Exaprom PDF is also open source, BSD protocol.

 

First download the toolkit, the download and installation instructions are at: https://decibel.ni.com/content/docs/DOC-10952. The author (Jean-Marc Simard, who is also a great god) posted on the NI forum and can see that he has been maintaining and is still answering some questions from the user. The following is basically a porter. The author produced two versions:

2013 version download address: https://forums.ni.com/ni/attachments/ni/3046/11150/4/Exaprom%20PDF2.0%20(LV2013).zip; 2009 version Download address: https://forums.ni.com/ni/attachments/ni/3046/11150/6/Exaprom%20PDF2.0%20(LV2009).zip. After downloading the archive, unzip it to get a folder and a file, as shown in the following figure: One is the .VI code package, and the other .mnu file is the menu file.


 

 

Next, place them in the specified directory: C:\Program Files\National Instruments\LabVIEW Version\vi.lib\ (Maybe it is a little different upon your Windows® OS version) Place the code folder here, refer to the below screenshot.


 

Then place the menu file, as shown in the following screenshot: C:\Program Files\National Instruments\LabVIEW Version\menus\Categories\Programming\, (maybe a little different upon your Windows OS version) as the name implies, it knows the specific location.

 

After you place all files into the specific locations and restart LabVIEW, you can see that the function panel has loaded all PDF-related functions. As shown the below:

 

Reading here, you should feel a lot of peace of mind. The author developed this toolkit entirely based on LabVIEW® and NI style and it very easy to use and start. In addition, you can also find that the author (Great God) has complete copyright notice information in each function's program panel and Help page - both itextsharp's copyright statement and the author's own BSD copyright notice.

 

Finally, is it feeling less or missing? Yes, it seems that there is no user instruction? In fact, the author has provided the very detailed help information for every function, as well as a very detailed user manual. The author is very clever to integrate the entire user manual into a VI. It is the function VI labeled in the next screenshot. After opening and running, it will generate a 43 page PDF document, which is a lot of pictures and text, and the User Manual.vi is full of the creation of the text and various instances of the PDF document. Just imagine: an example has generated an PDF document with 43 pages of illustrations. What else can't be done? If there is a higher requirement, or the discovery of bug, it can interact with the original author at the place where the article is published, and it can basically solve the general problem. Of course, with the progress of technology, PDF is also a further development, but it can be seen that copyright considerations, the author does not upgrade the itestsharp©, and can not be upgraded in the existing mode.


 

 

It is over here. It can be said that in addition to the author (myself) introduced this artifact(toolkit), and talked about copyright issues many times. It also promotes a kind of copyright awareness. Even if it is free and open source software, it is also required the agreement, such as signature, re-open source and so on. Therefore, if the software is developed through this article, not expect to label the copyright agreement everywhere, at least the copyright notice of itestsharp and Exaprom PDF is marked on the copyright page of the software. Again, the toolkit mentioned in this article can be used for closed-source commercial purposes without paying fees, and only the developer's copyright information needs to be retained. Well, the spread of this article also requested to retain the source and signature - WeChat® public number: LabVIEW-Jobs :-)

 

Reference:

1. https://decibel.ni.com/content/docs/DOC-10952 (Exaprom PDF release page)

2. Https://itextpdf.com/ (itestsharp official website)

3. Https://sourceforge.net/projects/itextsharp/ (itestsharp source code shared release page)

 

Note: This article is translated and reprinted from WeChat public account--LabVIEW-Jobs, please follow this WeChat public number for the original source inquiry. And any question about this article, please also contact with author by email support@itestgroup.com

 


Saturday, May 5, 2018

通过LabVIEW生成Excel的六种方法

概览

将NI LabVIEW软件中的数据移动到Microsoft Excel有许多不同的方法。 每种方法都有优缺点,因此我们将探讨一些可用的选项,以帮助您找到适合您应用的选项。

目录

LabVIEW生成Excel的方法比较表格

 
导出
TDMS文件
CSV文件
报告生成
DIY ActiveX
NI DIAdem
交互式

 

 

 

 

以编程方式

1

自定义格式化

 

 

 

未安装Excel时

 

 

 

自动保存元数据

 

 

 

 

需要额外的软件

 

2

 

3

 

4

基于文件的传输

 

 

 

自动化接口传输

 

 

1 数据可以以编程方式发送到Excel,但保存文件需要手动操作
2需要用于Microsoft Excel的TDM Excel加载项 - 可以免费下载并与最新版LabVIEW一起安装
3需要安装用于Microsoft Office的NI LabVIEW报表生成工具包
4需要安装DIAdem

 导出到Excel右键菜单

将可见数据从LabVIEW导入到Excel的最简单方法是:右击前面板上显示有要导出的数据的显示控件,然后选择"导出数据到Excel"。 

导出数据到Excel方法支持任何图形、图表、表格、数组或数字数据控件。 图形和图表仅导出可见数据,这意味着您可以使用图形工具来放大感兴趣的区域,并仅导出需要的数据。 表格仅导出当前选中的数据,而数组则可导出数组中的所有数据。

您还可以使用调用节点,以编程方式调用导出数据到Excel导出绘图数据到Excel方法。 以下代码片段可生成正弦波,然后将绘图数据输出到Excel两次,以显示两种不同的方法。 两种方法之间的区别是导出绘图数据到Excel方法仅导出指定图的数据,而导出数据到Excel方法则导出所有图的数据。 这个简单的例子只有一个图,所以这两个方法产生的结果相同。


使用这种技术时,请注意,Excel必须安装在与LabVIEW相同的机器上,并且无法通过编程来保存Excel文件。 因此,这种方法最适合于需要交互式调查数据并快速将数据发送到Excel进行分析或发布的应用。

注意: "导出到Excel功"功能从LabVIEW 2010版开始提供,此前的版本均不具备该功能。

保存为TDMS文件

NI开发了技术数据管理流(TDMS)文件格式来快速、高效地保存文档化的测量数据。 虽然TDMS本身不支持Excel,但是您可以使用一个免费的Excel加载项将数据导入Excel。

创建TDMS文件最简单的方法是使用文件I/O选板中的 Write To Measurement File Express VI。

与所有Express VI一样,将VI放在程序框图上时,会看到一个配置对话框。这个特定的Express VI可以不仅仅只是保存为TDMS,所以一定要在文件格式部分中选择二进制(TDMS)。 保存文件的方式有多种,当选定文件已经存在时的做法也有多种选择。


[+] 放大图片

您可以通过点击设置...按钮,使用基于时间或文件大小的计划表保存到一系列文件。

这时会产生一个非常简单的程序框图:

对于更习惯手动控制的用户,LabVIEW还提供了一个用于写入TDMS文件的API,而无需使用Express VI。

如果有数据存储到TDMS文件中,则需要确保您已安装用于Microsoft Excel的TDM Excel加载项。 安装LabVIEW时,您可能已经安装了该加载项,如果没有,您可以随时免费下载。 安装加载项后,您可以直接在TDMS文件上单击鼠标右键,然后选择 打开方式»Excel导入器,这时会打开Excel并显示相应的数据。

Excel中的第一个工作表包含了文件属性和其他元数据。


[+] 放大图片

每组通道都作为单独的工作表进行加载,每个通道的数据都显示在各自列中。


[+] 放大图片

数据导入到Excel后,就不会依赖或链接回原始的TDMS文件(但原始文件可以使用LabVIEW或DIAdem中的ExcelTDM DataPlugin重新创建),因此您可以随意与任何Excel用户共享您的工作簿。

 保存到CSV文件

大多数情况都支持逗号分隔值(CSV)文件格式,因此您可以在Excel中打开文件,但也可以将其导入到其他电子表格、数据库或分析工具。 CSV文件是人类可读的文本文件,列与列之间通过逗号隔开,行与行之间则通过换行隔开。 这通常需要我们在LabVIEW中进行一些数据操作,以便将测量数据转换为适当的格式,因为我们无法使用复杂的数据类型(如波形),也不能将数值存储更高效的二进制格式,以便LabVIEW或TDMS文件内部使用。

您可以使用文件I/O选板中的Write To Spreadsheet File VI来创建要在Excel中打开的CSV文件。

简单的一维数组并不需要进行任何额外的处理。默认情况下,Write To Spreadsheet File VI使用制表符(/t)作为分隔符,因此您只需要指定逗号(,)作为分隔符即可。

一个更复杂的例子是将Express VI返回的数据(如DAQ助手模拟信号)写入CSV文件中,并标记时间,同时在下一列显示测量值。 下面的代码片段显示了如何将动态数据转换为波形数组; 然后将数组中每个波形的所有测量值转换为字符串; 接着再为每个样本制定一个时间字符串; 并最终为这些字符串创建二维数组,以便传递给Write To Spreadsheet File VI。


[+] 放大图片

您可以使用Excel打开CSV文件,这时会看到数据按列和行正确分割。


[+] 放大图片

如果您使用上面的代码片段,Excel将会理解您的时间戳,但可能无法以有用的方式进行格式化 - Excel是为商业办公而开发的,通常无法在数秒甚至更短的时间内处理数据。 要解决这个问题,您必须使用自定义格式来格式化包含时间数据的单元格,如下所示。


[+] 放大图片

这种方法的一个缺点是此格式化信息无法保存在CSV文件中,因此每次将新文件导入Excel时都必须手动重复该过程。 虽然只能在Excel中打开一次,但您仍可以将数据保存为Excel文件来保留格式,以便后续使用。

Microsoft Office报表生成工具包

在将数据发送到Excel时,用于Microsoft Office的NI LabVIEW报表生成工具包提供了很大的灵活性。 最大的优点之一是您可以在Excel中创建一个模板工作簿,并将其保存为.xltx或.xlt文件,然后使用LabVIEW在VI运行时使用数据填充模板。 此代码段显示如何使用MS Office Report Express VI填充此类模板。


[+] 放大图片

创建模板时,您可以像任何其他Excel工作簿一样自定义格式。 然后将单元格命名为数据要放置的位置(对于表格或数组,您只需要命名左上方的单元格即可)。


[+] 放大图片

创建模板后,将Express VI指向模板,并告诉LabVIEW您希望数据如何显示在报表中(以表格或图表形式显示)以及是否要打开、保存或打印Excel文件。

运行上面的代码片段会产生如下所示的输出。 这个简单的例子介绍了这种方法的使用 - 顾名思义,报表生成工具包通常用于自动化生成完整的报表,而不是将简单的数据发送到Excel。


[+] 放大图片

除了Express VI之外,报表生成工具包还提供了一个可用于自动化Excel的完整API。 下面的示例代码产生的输出类似于上述示例,但不需要模板工作簿。 此外,该示例不是使用LabVIEW图形的图像,而是使用Excel图表工具绘制图形。


[+] 放大图片

运行上面的例子得到以下输出:


[+] 放大图片

 DIY ActiveX/.NET

报表生成工具包基于Excel ActiveX接口。 您可以通过直接ActiveX调用或Microsoft.Office.Interop.Excel .NET程序集自动创建Excel文件来使用此API。 下面的代码片段生成与Report Generation Toolkit示例基本相同的结果,但是使用的是.NET互操作程序集来与Excel进行通信。 可以看到,代码最后更为复杂,但任何有ActiveX/.NET编程背景的人员都不会觉得陌生。


[+] 放大图片

 

以下是上述代码片段的输出:


[+] 放大图片

 DIAdem作为替代选择

如果您有更高级的数据需求,比如较大型的数据集、大量的文件或特定的报告需求,还可考虑DIAdem。 DIAdem是一款用于快速定位、分析和报告测量数据的工具,通常更能够满足工程师对数据工具的许多需求。

如需了解更多关于使用DIAdem而不是Excel提高工作效率的信息,请阅读本文


Reference

--------

  1. 本文转载至NI官方文章,如有侵权请联系admin删除,来源地址:https://www.ni.com/newsletter/51339/zhs/
  2. 技术探讨可联系support