在线座谈

热门关键字: 能量 有源 CODEC EDI 

关于本次座谈

座谈简介

电场(E-field)感应技术是一种新型探测技术,能够感应弱电场和检测电场变化,可以帮助设计人员开发需要非接触感应的嵌入式系统。本次在线座谈将主要阐述飞思卡尔的电场感应芯片,以MC33794/34940为主。首先我们将讲述什么是电场、什么特性会影响电场的行为以及我们如何以此来开发具有独特价值和多种用途的行业应用。接下来,我们将介绍飞思卡尔产品的特点和功能,并阐明其领先的特性。最后,座谈还将提供以我公司产品作触摸屏应用的示例以及在系统开发和按键设计中的注意事项。同时,我们还将带您领略更多有关我公司电场感应器件的应用意念,例如水位检测或靠近检测。快来加入我们的行列,不要错过这些激动人心的技术和电场的感应。

精彩问答

主题: 电场感应技术揭秘及其应用– 飞思卡尔推出业界首款电场感应器件
在线问答:
[主持人:ChinaECNet] 各位听众(网友),上午好!欢迎参加中电网在线座谈。今天,我们有幸邀请到Freescale公司的专家就“电场感应技术揭秘及其应用– 飞思卡尔推出业界首款电场感应器件”举行在线座谈。在座谈中,您可就您关心的问题与Freescale公司的专家在线进行直接、实时的对话交流。中电网衷心希望通过大家的共同努力,不仅能够增进各位听众(网友)对“电场感应技术揭秘及其应用– 飞思卡尔推出业界首款电场感应器件”的了解和掌握,而且能够为大家事业的发展带来裨益。  [2006-6-22 10:42:36]
[问:elmer] 为什么称为“业界首款电场感应器件”,和现在的触摸键盘的原理有什么区别? 
[答:飞思卡尔] 飞思卡尔是第一个提供电场原理的感应器件的公司。 请注意我们的触摸键盘是利用电场原理来实现的。 [2006-6-22 10:51:21]
[问:Mr Wei] 如果我想做一个触摸感应按键,那触摸电极是买的,还是自己做?你们有没有这方面的技术资料! 
[答:飞思卡尔] 您的触摸电极是由您自己购买的。 从飞思卡尔今天讨论的内容中,您会发现如何设计和实现电极,尺寸和布线的问题都有讨论。 [2006-6-22 10:53:07]
[问:wang guangsheng] 请问:电场感应技术能否用于精密定位?谢谢! 
[答:飞思卡尔] It depends on how accurate you need. Most electrode sensitivity may not be very high. It is hard to be very accurate. [2006-6-22 10:56:15]
[问:elmer] 能否介绍一下微波炉溢出检测时如何实现的 
[答:飞思卡尔] 当有液体溢出到微波炉表面时,相当与有靠近的导体,这会使感应电极的感应发生较大的变化,利用这个变化来实现检测。 [2006-6-22 11:00:11]
[问:pguomin] 能否利用电场感应来检测物体移动的方向和移动速度,谢谢 
[答:飞思卡尔] Yes. It can be used to detect body moving direction and speed by getting signal from electrodes which at designed position and direction. [2006-6-22 11:01:11]
[问:qingfengxuri] 电极是否适应PH酸性环境? 
[答:飞思卡尔]  电场传感器的一个优势就是恶劣的工作环境,辐射,腐蚀,高温,等等。 适当的涂层介质可以很好的起到保护和加强感应灵敏度的作用。 请看此在线座谈讨论材料中的相关部分,有详细的介质材料介绍。 [2006-6-22 11:03:14]
[主持人:ChinaECNet] 我们已经进入问答阶段如果听众想重温演讲或内容可以点击下面“回顾演示”重看演讲。  [2006-6-22 11:03:33]
[主持人:ChinaECNet] 在此回答问题的专家是Freescale公司的:Helen Lu、Norman Chan、Robin Ma、Harvey Wong、Harriet Mak、Vincent Ko和Ernest Chan。  [2006-6-22 11:04:16]
[问:lemys] 我对使用电场原理的感应器件的优势还是不是十分明白,请说明 
[答:飞思卡尔] 其中一个就是非接触式感应,可以减少机械磨损;另一个是可以远程放置按键,可以在不同的恶劣环境中使用等等,请看此在线座谈讨论材料的相关部分。 [2006-6-22 11:05:06]
[主持人:ChinaECNet] 各位观众,现在用户提问很踊跃,专家正在逐一回答。请耐心等待您问题的答案,同一问题请不要多次提交。  [2006-6-22 11:06:09]
[问:lzmxl] 请问:1.若用该器件构成一个简单的接近开关,它的最大感知距离可做到多少? 2.如果做一个4×4的(手)感应键盘,最小可以做到多大? 
[答:飞思卡尔] a. Please tell me how about the sensing distance of it, if we build a simple proximity switch with this device. b. This depends on the size and material used for the electrode. We can achieve 50cm of distance for electrode size that is almost the size.   [2006-6-22 11:08:44]
[问:qingfengxuri] 请问触摸感应技术在成本上是否高于其他触摸技术?从设计角度上是否合适? 
[答:飞思卡尔] 成本的核算和您的系统设计整体有关,前期和后期维护也有关,飞思卡尔对电极的材料的要求不多,仅和布线,大小等有关。请和飞思卡尔的销售代表联系获得价格方面的信息。从设计角度上来说,利用飞思卡尔的电场传感器的触摸键盘技术是十分适合的。它的优势主要在无机械磨损,感应灵敏度可以保持长期一致,适合远端使用,适合恶劣的化学环境和其它环境。 [2006-6-22 11:09:09]
[问:c13355077] 是否可以采用冰箱靠近的例子来做防非法入室的应用? 
[答:飞思卡尔] Yes. You may install several electrodes in several place where the way people have to go through if they go in the room. Then you can know some one come in. [2006-6-22 11:09:37]
[问:zhjincheng] mc33794,可以用做移动探测吗,您可以列举几个详细例子吗 
[答:飞思卡尔] The moving area has to be designed in advance and electrode to be installed where the place indication. When the body move the A place, the electrode A / channal A will have output, when its move to B electrode, B will response. Plus timer, you may also the time the body move from A to B. [2006-6-22 11:14:15]
[问:lgh8102] 请问你们触摸键盘和普通键盘的优势和区别在哪些方面 
[答:飞思卡尔] For buttons more than 6, E-field solution is more ecnomic. [2006-6-22 11:16:43]
[问:zhjincheng] 我想详细了解下,mc33794技术特点 
[答:飞思卡尔] 您的问题范围太大了。 您可以从在线座谈讨论材料中发现主要的特点,更详细的技术参数和信息,可以参看MC33794的数据手册,在手册上给出了您需要的所以技术规范参数。 如果您还有问题,请直接和飞思卡尔在当地的办事处或代理商联系。 [2006-6-22 11:18:02]
[问:pguomin] 为了检测高速移动物体的速度,我在A点到B点放二个极,但由于在读取电极时需延时1.5ms,难以读到标准值,有否解决这延时问题,或有其他更好的办法? 
[答:飞思卡尔] We can discuss this off-line. We will reply in details later. [2006-6-22 11:18:48]
[问:qingfengxuri] 请问灰尘的堆积会否日益影响电极的工作? 
[答:飞思卡尔] Regular calibration will help on this. [2006-6-22 11:20:45]
[问:wanfay] 请问Freescale 的电场传感器是基于何种原理?和基于晶体电光效应的电场传感器有何不同? 
[答:飞思卡尔] 飞思卡尔的电场传感器基于的原理在此在线座谈的讨论材料中已经详细的介绍了,如果您还没有来得及观看,请回放。 关于和其它原理的传感器的比较,例如您提到的晶体光电效应传感器,我不了解它的原理和输出方式,无法给您一个答复。您可以对比我们的产品规格和其它产品的规格来找出不同。也可以在本次讨论结束后,和我们当地的技术服务工程师联系,进一步讨论。 [2006-6-22 11:21:54]
[问:w223456] 拟将mc33794应用于自动门安全探测,请教如下问题: 1、mc34940也有类似功能,为什么国内买不到? 2、以前的实验发现,探测结果受环境湿度影响较大,有何补偿妙招? 3、实验发现,当极板附近有(不接触)导体时,电场会沿导体传导。这意味着,当极板安装在金属门框上时电场会沿金属门框传导,结果导致探测器误报警,实验结果也是这样。请教有何屏蔽良方? 
[答:飞思卡尔] This is already out for sampling, you can contact the local Freescale Sales/Support group in China or talk to our distributor in your region like Avnet, Arrow, Future etc. I will feedback to our support group why this is the case. Sorry about this. 2. Previous experiments show that the detection results is greatly influenced by the ambient humidity. Do you have good method to compensate it? It depends on your application. If you are sensing a big object like a person, or even a finger then the calibration of doing a background reading of the environment would help you account for the humidity. If you are sensing a very small object or change in the electric field then we would need to understand how much accuracy do you need and work from there with our expert group. 3. Experiments show that electric field will transmit along the conductor when there are conductors near the plate. Therefore, when the plate is located over the metallic doorframe, the electric field will transmit along the metallic doorframe, which will result in false alarm. So does the experimental result. Do you have good method to shield? Thank you. Yes we have a shield pin, feature on our chip that will prevent the leaking of the e field energy. You can use another copper/conductor that connects to this pin and mask the conductor of interests, hence shielding it from the door frame.   [2006-6-22 11:21:59]
[问:elmer] 请问,断续液位测量时,电极是否接触液体? 
[答:飞思卡尔] No. The electrode should be put outside of the liquid container. [2006-6-22 11:22:08]
[问:eeszh] 请问国内现在能买到MC34940的开发套件吗?  
[答:飞思卡尔] 可以,请和飞思卡尔的销售代表或代理商联系, 联系方式: http://www.freescale.com.cn/others/wheretobuy/ [2006-6-22 11:22:59]
[问:sss3333] 从那可查到详细的电极设计资料? 
[答:飞思卡尔] You may get some inf. from FSL AN1985. It can be downloaded from FSL web.  [2006-6-22 11:25:45]
[问:hdq] 请问提供工业级芯片吗?我们希望把其应用于铁路车载设备,谢谢! 
[答:飞思卡尔] Current products are -40C to +85C. [2006-6-22 11:29:30]
[问:zhangwq] 电场感应器可以做感应无线鼠标产品? 
[答:飞思卡尔] No. It is not sensitive enough. [2006-6-22 11:30:03]
[问:wuhuxianren] 电场感效应器件有没有特殊电源要求; 是否特别需要注意EMC等问题,如何解决的; 恶劣环境的反应如何; 
[答:飞思卡尔] 外界的干扰对我们的测量是有影响的。在飞思卡尔的讨论中告诉大家我们的器件提供多种方式对干扰进行屏蔽或弱化。例如,内部的高纯净正弦波发生器,屏蔽信号驱动,不工作的电极自动接地等等。这些器件本身的特性帮助您的产品更好的通过EMC。 我们还介绍了如何布线以减少线缆间产生的干扰。选择合适的介质材料可以有利于您的产品感应的灵敏度和对恶劣环境的适用。 对电源的要求和其它产品一样,没有特殊的要求,器件内的5伏调节器可以保证器件的供电,利用外部的REF_A/B和其它电阻电容可以精确的控制器件的工作。请看数据手册。   [2006-6-22 11:30:27]
[问:falling74] 评估模块KIT33794DEVM包括那些内容?它的价格是多少?货期呢? 
[答:飞思卡尔] You can get KIT33794DWBEVM details from following website. For price and lead time, please contact Freescale distributor or local sales office. http://www.freescale.com/webapp/sps/site/prod_summary.jsp? code=KIT33794DWBEVM&parentCode=MC33794& nodeId=0112698268 [2006-6-22 11:32:27]
[问:Xihuwuyu] 您好,能不能再解释一下屏蔽驱动?是怎样实现呢? 
[答:飞思卡尔] 是飞思卡尔同时在屏蔽驱动引脚驱动一个和电极相同的信号 (同相和同幅度), 这样可以减少在线缆传输时随机引入的干扰的影响,进一步降低噪声。 [2006-6-22 11:32:56]
[问:xymzju] 1、MC33794能否测量含有电解质的液体? 2、能否用一个电极来测量液位相对高度(高于或低于电极)? 3、对电极的面积有没有要求? 4、当电极与周围电路距离较近时,如何消除周围电路、芯片、PCB板的布线等对电极的影响? 5、如何消除人体靠近时对被测电场的影响(例如手靠近电极但未接触)?  
[答:飞思卡尔] a. Yes, it can but using electrodes. b. It can be done and there are various ways of doing. One easy method is to place a strip, or 2 strips of copper along the height of the container. c. Not really, the bigger the better. But you should ensure that the net capacitance is not larger than 100pF d. It is not easy to explain this here, please read our application note AN1985. But the main thing to keep in mind is to keep the non sensing element like PCB traces short and to use a shield (our device has a shield pin) to shield these traces. Software calibration can also be done on a regular basis, abit like auto zeroing which will eliminate the surrounding elements. e. You need to set a threshold value that is bigger than when the hand gets close to the electrode. I am assuming that you are detecting something very large? However, if this is not then there’s nothing that you can do as human makes great dielectric capacitance and will short the e field to ground if the finger or hand is very close to the electrode.   [2006-6-22 11:34:08]
[问:sss3333] 多电极和单电极相比有何优势?在设计上如何选取? 
[答:飞思卡尔] 当您看完此在线座谈的讨论材料后,您会了解到:多电极可以使感应的测量数量增多,超过我们提供的9个电极。 满足更多产品的需要。 在设计时可以根据您的测量要求,选择1个电极,2个电极或3个电极来测量一个感应信号,通常我们不建议适用更多的电极来测量一个信号,这是因为随着电极数的增多,每个电极的感应变化量会相应的减少,检测的灵敏度会降低。 [2006-6-22 11:36:17]
[问:ciber] MC33794的灵敏度有多高?能检测到电容的变化是多少?或者说它的接近距离有多远? 
[答:飞思卡尔] 可以检测10-100pf的电容。距离可以达到几米(利用屏蔽驱动信号)。  [2006-6-22 11:38:14]
[问:james_ou] 在不同的環境條件下, 感應的結果會不會有明顯的差異, 如何補償 ? 
[答:飞思卡尔] 不同的环境对感应的影响可能会有一些影响。可以通过加大感应面积,缩小感应距离,适用高介电数的介质材料来实现。 如果设计无法改变,通过设置不同的阀值来监控变化,一定程度上增加测量的准确性。 [2006-6-22 11:42:32]
[问:josip] MC33794用于位置识别时,测量最大距离范围是多少?另外哪些物体它无法识别?可以测量到物体的外形轮廓吗? 
[答:飞思卡尔] We have not tested the max distance range as this depends on the materials, electrode size, environment etc. But we have achieved 50cm of proximity range using a 8x12 inch electrode size. However, for positioning indicator you can place electrodes at various distance away from the target object. Similarly for profile, detection is possible and you need to place electrodes around the space that you expect the object will be in. Objects that are solely none conductive and has a very very weak path to ground can not be detected. [2006-6-22 11:43:31]
[问:wanfay] MC33794最多能设计多少个电极?最多能控制多少个节点? 
[答:飞思卡尔] 9 electrode. You may use multiplising/time sharing to upgrade to 45, even 81... [2006-6-22 11:43:58]
[问:elmer] 用于检测水位的电极能否在容器外? 
[答:飞思卡尔] Yes. Its outside of water tank. [2006-6-22 11:44:49]
[问:kenh1] Can I get schematic for water level sensor application? How deep and accurate would this device be. I am interested in measuring from 1 foot to 30 feet. 
[答:飞思卡尔] Please contact Freescale support group for this. We can help you with this as we have application circuit that can do this.   [2006-6-22 11:44:56]
[问:jlspwdy] 汽车仪表中的车速里程表的小计里程和总计里程的切换目前是用归零键开关,可否用触摸感应技术放在仪表的表玻璃上,以方便司机调整?成本能增加多少? 
[答:飞思卡尔] 可以使用,但是需要考虑的是如果是误操作,或误靠近该按键时如何保证正确的问题。 关于成本,可以和我们的销售代表或代理商联系获得详细的价格。 [2006-6-22 11:45:08]
[问:foxr23] 如何組成多個電場感應器的應用? 
[答:飞思卡尔] 可以利用1个电极,2个电极,3个电极来测量一个感应信号。 这样的组合可以远远多于芯片提供的9个电极。 [2006-6-22 11:46:19]
[问:foxr23] 電場感應器輸出的DC level 為何? 
[答:飞思卡尔] This is because the modulation on the e field is measured by a rectifier and then low pass filtered. This give rise to a DC level and depending on this level is the change on the e-field. [2006-6-22 11:46:53]
[问:Mr Wei] 请问做触摸感应的电极价位一般在多少! 
[答:飞思卡尔] 您可以看到飞思卡尔介绍的电极其实就是有一定面积和形状的薄的导电材料,如铜箔或其它金属箔等,成本不高。 [2006-6-22 11:47:57]
[问:lemys] 具体应用的详细DEMO什么时候能推出?成本方面呢,我认为你们应该带一名销售,一站式服务多好. 
[答:飞思卡尔] Can you specify what application demo you need? For cost, please contact Freescale distributor or local sales office. [2006-6-22 11:48:24]
[问:c13355077] 可以用来测量入室盗窃的例子吗?如何布置电极? 采用何种形式的电极? 
[答:飞思卡尔] Yes it can be used. One such way is the place strips of copper sheets on the floor that is covered by an overlaying material to hide it. So when some one has stepped on it then a change on the electric field will be detected.   [2006-6-22 11:49:26]
[问:熊劲松] 触摸感应键盘可以用全金属的吗? 
[答:飞思卡尔] Not whole pannel, but pad can be metal. [2006-6-22 11:49:33]
[主持人:ChinaECNet] 所有问题均已提交给Freescale公司的专家。座谈期间未回答的问题,Freescale公司专家也会逐一回答,并在中电网上公布,请大家注意收看。  [2006-6-22 11:51:52]
[主持人:ChinaECNet] 由于时间关系,本次中电网“在线座谈”马上就要结束了。虽然各位听众(网友)已与Freescale公司的专家讨论了许多问题,但是还有许多提问没有来得及进行交流。本次在线座谈结束后,中电网将请Freescale公司的专家继续答复所有的来自各位听众(网友)的提问,然后整理上载到中电网网站上,以便大家查阅。  [2006-6-22 11:52:08]
[问:david_m_godfrey] is there a positive way to detect if the electrodes become wet, ie there is low resistance between electrodes 
[答:飞思卡尔] Yes. There are many ways and it depends exactly on your requirement. For example if it is spillage then you need design electrodes placed apart so that when liquid falls on both electrodes detection is made. If you are using just one electrode then the difference between liquid and air would make a different to the efield as they have different dielectric constant, but the electrode needs to be big. [2006-6-22 11:54:43]
[问:moving2] 你好!我们的一个客户的一个产品,需要用电场传感器来开发,但是不知道33794的性能是否能够达到客户的需求:在一个大小为1米×2米的区域内,用手指点击这个区域内的某个位置,要能够感知到手指所在的具体位置。 
[答:飞思卡尔] You need to divide the 1mx2m to many small area and numbering them. Then you may know which number area the finger pointing. [2006-6-22 11:55:20]
[问:gaoyuanci] 对于人的手感应距离是多远。是否可以免费申请样品 
[答:飞思卡尔] We have not tested the max distance range as this depends on the materials, electrode size, environment etc. But we have achieved 50cm of proximity range using a 8x12 inch electrode size. Pls contact our distributors or Freescale support or sales office for free sample.   [2006-6-22 11:56:21]
[问:james_ou] 請問抗 ESD 能力如何 ? 
[答:飞思卡尔] 2kV HB ESD. [2006-6-22 11:57:10]
[问:dvssy] 在触键开关方面,传统机械按键,在成本上有很大优势,那么MC34940在价格方面如何面对这一问题。 
[答:飞思卡尔] It depends on the number of button. E-field solution is strength on button more than 6. [2006-6-22 11:59:47]
[问:pentiumxm] 可以检测的电场强度 范围,距离等 
[答:飞思卡尔] 飞思卡尔的芯片利用的是电容器原理。靠近的物体是电热器的一个电容板,电极是另一个电容板。感应的范围是10pf到100pf之间的电容,超过范围比较难检测。根据电容器的公式,和距离,面积,介电常数等有关。 所以增大面积可以是感应的距离增大,使用高介电常数的介质材料可以增大电场的强度,便于测量。 [2006-6-22 12:00:26]
[问:huihe] 我想测墙体内的导线有无电压,墙体厚10cm,能否用此IC? 
[答:飞思卡尔] Pls contact Freescale upport/sales office for samples and buying this IC. It is available to the market. It is not used to measure a voltage change on the conductor but a capacitive change.   [2006-6-22 12:00:27]
[问:elmer] 电场感应用于微波炉检测沸溢时如何实现的? 
[答:飞思卡尔] Yes. There are many ways and it depends exactly on your requirement. For example if it is spillage then you need design electrodes placed apart so that when liquid falls on both electrodes detection is made. Pls contact our support/sales office for further help. [2006-6-22 12:01:50]
[问:wangzhong jie1023] 电场感应技术在触摸板应用中精度能达到多高呢?谢谢! 
[答:飞思卡尔] Yes we have solution for liquid level detection. But for oil and petroleum this is not so effective as the dielectric constant is rather low. You need to test this out first. [2006-6-22 12:05:13]
[问:ciber] MC33794中的虚拟地是如何实现的?要注意什么问题? 
[答:飞思卡尔] The virtual ground is not implemented, it is part of the environment, hence the floor or ground. What you need to ensure is a conductive path to this like a human person. [2006-6-22 12:06:40]
[问:烈火旋灯] 由于每个电极的输出电平并不是一样的,和很多因素有关,是不是就意味着每个产品都需要在安装现场做调试,这会不会限制了电场传感器的应用 
[答:飞思卡尔] No, you need to perform a software calibration when you turn on the device. This will takecare of the different e-field loading for different electrodes. [2006-6-22 12:09:52]
[问:] a. 电场感应的距离? b. 电极的大小,形状有没有限制? c. 对另一个电极产生的电场响应速度有多快?
[答:] a. This depends on the placement of the electrode, material used, method used. If you are doing it in free space or air then the distance can be 50cm or more for a copper sheet of size A4. b. Not really. But again it depends on what you are trying to achieve, are you detecting a large object, or a small touch panel, or a slider control? All this will concern with your shape and size. If you are talking about touch panel application then we do. The rule is that the bigger the electrode sizes the more sensitive or effective the performance. c. This depends on a number of factors like loading, ADC, MCU, and your software algorithm too and what capacitor you put on the LP_cap pin. But for the sensor itself it is typically around 500us to 2.5ms based on the LPF and the LP_cap pin loading.
[问:] a. 电场感应的原理? b. 电场感应与电磁感应有什么区别? c. 电场感应主要用于那些电路? 起什么作用? 有什么好处?
[答:] a. Basically, the e-field sensor generates a 120KHz signal and then detect the nearby object through the change in capacitance along the selected electrode. b. The e-field sensor is based on measuring the capacitance change as mentioned above. Electromagnetic induction may arise from the motion of a conductive material under the magnetic field. c. There are wide range of applications such touchless keypad, liquid level detections and more. Advantages are contactless and no mechanical wear out & higher durability, etc. Please refer to our webcast material for more information.
[问:] 电场感应的灵敏度?
[答:] It can measure capacitance of about 10-100pf.
[问:] Can you suggest an electrode layout to put on the outside of a 10mm thick plastic water tank wall?
[答:] There is no special requirement for this. If you are just trying to detect liquid height, can use 2 strips of metal placed on opposite end of the container (assuming it is round), so that it forms a cap with the liquid content in between - though its inside the container and not touching the liquid). Pls refer to our app notes AN1985.
[问:] could we download this ppt?
[答:] 请在以下网站选择"已存档的在线座谈" 的 "飞思卡尔的电场感应技术揭秘及其应用在线座谈", 您便可回放在线座谈: http://seminar.chinaecnet.com/seminar/cn/seminarclear.asp
[问:] could you send me a copy of your todays presentation for me, thanks a lot!
[答:] 请在以下网站选择"已存档的在线座谈" 的 "飞思卡尔的电场感应技术揭秘及其应用在线座谈", 您便可回放在线座谈: http://seminar.chinaecnet.com/seminar/cn/seminarclear.asp
[问:] how can I download the slides/presentation for later reference?
[答:] 请在以下网站选择"已存档的在线座谈" 的 "飞思卡尔的电场感应技术揭秘及其应用在线座谈", 您便可回放在线座谈: http://seminar.chinaecnet.com/seminar/cn/seminarclear.asp
[问:] How fast does it detect a change on electric field?
[答:] This is at the limitation of your software scheme and ADC used. Also depends on a number of factors like loading, ADC, MCU, and your software algorithm too and what capacitor you put on the LP_cap pin. But for the sensor itself it is typically around 500us to 2.5ms based on the LPF and the LP_cap pin loading.
[问:] How to sense water level with this?
[答:] Water is a "good" material to be sensed. In this webcast, we introduced a demo to measure water level using the nine electrodes of MC33794. We also introduced how to improve the sensitivities of each electrodes. Please review the webcast materials, or contact our local representatives for more support.
[问:] I would like to know the technology behind the touch screen displays.
[答:] There are different types of technology for that. If it wants to use the e-field sensor for such application, it needs to consider how to construct electrodes into the screen surface. It also needs to consider how fine the resolution is required. More than one e-field sensor devices may be needed to increase the resolution.
[问:] In using the efield chip for checking water tanks levels, is it necessary to use an external element?
[答:] It can use metal to make the electrodes and place them outside the water tank. Please refer to our webcast materials about the operation principle of that.
[问:] MC33794内部产生的正弦波频率范围是多少? 它如何优化到125kHz?
[答:] The external resistor attached to R_OSC pin control the center of frequency. Using a 39K ohm resistor can set the frequency to the optimizsed 120KHz frequency.
[问:] 被测物体与测试体之间距离有10cm,中间有介质(如水泥),如何准确测出被测物体的电场大小,如有几个被测物体彼此之间距离很近,如何区分?
[答:] First you need to attach an electrode plate to one of the electrode pin. You need to experiment on what size electrode (copper) is needed as this depends on the size and material used for the object and amongst other things like the dielectric. I f you are using cement, you need to know what is the dielectric properties of this. If it completely shields the electrode from the object then this solution will not be feasible. Secondly, if you have several objects, you need to use several electrodes so that you have it like a grid arrangement. Each electrodes are so small that they can detect if an object is near by or not.
[问:] 传感器精度如何?
[答:] It can detect capacitance of around 10-100pf.
[问:] 此器件与霍尔器件区别在哪?
[答:] Efield sensor is different as it is based on an applied voltage to a electrode and in turn creates an electric field. Hall sensing is concerned with a magnetic field and when a current-carrying conductor is placed into a magnetic field, a voltage will be generated perpendicular to both the current and the field. This principle is known as the Hall effect.
[问:] 电场传感器的响应时间有什么因素来决定? MC33794的响应时间有多快?
[答:] 外接电容LP_CAP连接到芯片内部的低通滤波器,和内部的50K欧姆电阻一起控制电极电平的输出和响应时间。 接10nF电容的响应时间约是1.44ms.器件要求你在读取输出电平时,至少延迟1.5ms。 而当使用1nF电容时,响应时间约4.5ms。 通过调整LP_CAP可以在一定范围控制响应时间。
[问:] 电场感应技术在汽车仪表中应用前景?
[答:] 目前电场感应用於汽车的 Airbag 及防盗器之用, 没有用於汽车仪表中。
[问:] 电场感应可以运用到民用的哪些方面呢? 具体来说。
[答:] 具有一定的节电常数的物体都可以感应。 在民用领域,各类家电的按键,安全使用保护,智能控制,遥控,门禁系统,等等。 在我们的讨论材料中有一些应用的介绍。
[问:] 电场感应器件是非接触感应,那么其最大感应距离多大?和电极面积有关系么?在键盘上是否会产生误感应?
[答:] It is hard to give you a number on the limit of this device as you have not accounted for the setup, material used, object size etc. To give you an example, using one electrode of A4 size can detect a range of 50cm. But if you need much more than this then you should use more than one electrode spaced apart by the distance of your concern. And also the distance does depend on the electrode size, material, what's the medium etc.
[问:] 电场感应在哪里会用到, 这次座谈有没有想应的资料, 留一份, 只听一次是记不好的。
[答:] 您可以下载本次座谈的材料,电场传感器可以使用在工业,汽车,消费类等领域。
[问:] 电极上积累电荷对于测量有何影响? 如何消除这种影响?
[答:] Although there is a 120KHz signal generated along the electrodes, the electrodes seldom accumulate charges after use. Also, the electrode outputs E1-E9 are grounded through internally resistors when not selected.
[问:] 对感应按键的误操作有没无解决方案?
[答:] Please visit the following web on a reference design of touch pad using our e-field sensor: http://www.freescale.com/webapp/sps/site/prod_summary.jsp? code=RDMC33794&parentCode=MC33794& nodeId=0112698268
[问:] 高温或长时间工作时对电阻等性能影响如何克服?故障诊断如何解决?
[答:] Normally, a software calibration can be done on the electrodes after power up. The effect of drifting environmental conditions can be compensated by taking the calibration process again in a perodical manner.
[问:] 接口标准是否完善? 兼容性如何? 如何保证应用中无缝使用?
[答:] The e-field sensor can interface to MCU by connecting the A,B,C,D pins to MCU I/O for selecting the electrodes, then the LEVEL pin to MCU's ADC pin to measure the output voltage of the selected electrode.
[问:] 可以分辨雪雨雾吗?
[答:] It should be able to distinquish between rain and fog, but not so well with snow. This depends on the layout design of your electrode and dielectric of the medium. The key thing is the use of dielectric constant property change when the medium has changed - from foggy to dry air etc. There is a factor of 80 difference between air and water, and a factor of 3.2 for air and ice.
[问:] 可以应用于控制 切割金属板的割枪的高度控制吗?也就是感应出金属板的距离吗?
[答:] I am not sure what you are asking here. It seems like you want a creative solution given for your torch application. If you want to measure distance between 2 metallic plane, you could by placing strips of electrode along the length of distance and take readings on the change. But if you want precise measurements and the metallic planes are of various sizes then this could be a concern.
[问:] 可以应用在哪些场合?
[答:] 请在以下网站选择"已存档的在线座谈" 的 "飞思卡尔的电场感应技术揭秘及其应用在线座谈", 您便可回放在线座谈: http://seminar.chinaecnet.com/seminar/cn/seminarclear.asp
[问:] 利用MC33794能否在近距离 1cm 处检测出移动物体的速度?
[答:] This depends on what range of speed? If the speed is not very fast, like in milliseconds then yes, it can. Just place 2 thin strips between the 1cm distance. The response time of the sensor is about 1ms so you need to account for your software, mcu, ADC conversion time, any loading etc.
[问:] 能否把演讲资料转到我的邮箱中?
[答:] 请在以下网站选择"已存档的在线座谈" 的 "飞思卡尔的电场感应技术揭秘及其应用在线座谈", 您便可回放在线座谈: http://seminar.chinaecnet.com/seminar/cn/seminarclear.asp
[问:] 拟将MC33794应用于自动门安全探测,请教如下问题: a. MC34940也有类似功能,为什么国内买不到? b. 以前的实验发现,探测结果受环境湿度影响较大,有何补偿妙招? c. 实验发现, 当极板附近有(不接触)导体时, 电场会沿导体传导。 这意味着, 当极板安装在金属门框上时电场会沿金属门框传导, 结果导致探测器误报警, 实验结果也是这样。请教有何屏蔽良方?
[答:] a. MC34940是一款较新推出的产品,请和我们的销售或代理商联系。 b. 一种方法是当湿度比较大时,可以通过校准功能来软件实现补偿。利用我们提供的两个参考输出引脚。 c. 可以尝试使用屏蔽层驱动来隔离附近的导体。
[问:] 普通的磁珠是不是电场感应器件?
[答:] If you are talking about magnetic then this is different to electric. So the answer is No. But if your question is asking if our eField sensor can sense the bead then yes as it a conductive object.
[问:] 请问电场感应技术的应用前景如何? 它在电磁兼容方面能有什么特殊创造吗?谢谢.
[答:] 电场感应技术的应用领域非常广,从工业,消费类产品到汽车产品中,都可以使用。 它的电磁兼容性符合工业,消费类和汽车应用的要求。
[问:] 请问,能够测量微弱的电磁场信号? 这种电场感应器件,与传统的磁棒线圈有着那些本质的区别?
[答:] 此种电场感应是由IC内部发出一固定频率来侦测外部物体与传统的磁棒线圈所流过的电流而造成的电场有所不同。
[问:] 请问MC33794和MC34940原理本质上是不是一样的? 他们具体功能上有什么区别?
[答:] MC33794和MC33940在原理上是完全一样的。 主要区别在于后者”减掉“了一些功能, 比如提供较少的感应电极(7个), 所以会在成本上有一定的降低, 满足需要较少感应节点需要的应用。 请参看它们的数据手册获得更详细的信息。 也可以和我们当地的销售代表联系。
[问:] 请问能否将相关提供视频资料的下载或者提供光盘?
[答:] 请在以下网站选择"已存档的在线座谈" 的 "飞思卡尔的电场感应技术揭秘及其应用在线座谈", 您便可回放在线座谈: http://seminar.chinaecnet.com/seminar/cn/seminarclear.asp
[问:] 请问什么是电磁感应器件?用在什么地方?
[答:] 如果您还没有观看我们的网上讨论的内容,请到网页上下载,有中文和英文两个版本。 在这份文件中,我们详细介绍了我们的电场传感器的原理和应用。
[问:] 请问这种电场感应芯片在工业应用中,比如接近开关、轻触按键等,能否通过EMC测试?有没有应用实例?
[答:] The low harmonic contents of the internal generated 120KHz signal is to minimize the interference to outside circuits. External source of noise may interfere to the e-field sensor, proper shielding on the electrodes can help on this. A good design of board layout and adding of proper filtering circuit can improve the overall EMC performance.
[问:] 請問 noise 對電場感應器的影響有多大?
[答:] We need more specific details to answer this. When you talk about noise, what types of noise and what frequency band? If you have a 120kHz noise that is coupled to the electrode then yes it will affect the reading but whether this concerns you would depend on the noise amplitude and your system resolution requirement. But this can be removed by appropriate filtering techniques. We chose 120kHz for our device because there's hardly any application circuitry that uses signal in this range. There can be so many source and types of noise in the world, it is beyond the scope of this web cast. Most likely an induced voltage noise will just modulate the 120Hz signal on the electrode. If the noise frequency is very high, the internal filtering of the IC would have dealt with this.
[问:] 請問電場感應器如何使用在觸摸屏上? 如何與MCU一起使用?
[答:] 可将此电扬感应器的电极放於屏幕下方做为侦测触摸之用, MCU做为侦测讯号强弱及谝码用。
[问:] 如果用电场器件 (如MC33794等) 检测汽油的高度是否可行? 如可行需要注意如何保证测量结果的稳定和准确? 谢谢!
[答:] 汽油的介电常数比较小,检测起来相对于水比较困难,您可以通过增大电极的面积,使用更大介电常数的介质等方法来提高灵敏度,同时注意电极布线的方式,这些在我们的座谈中都有介绍。
[问:] 我对这次研讨会很有兴趣,能否把演讲稿给我一份?
[答:] 请在以下网站选择"已存档的在线座谈" 的 "飞思卡尔的电场感应技术揭秘及其应用在线座谈", 您便可回放在线座谈: http://seminar.chinaecnet.com/seminar/cn/seminarclear.asp
[问:] 我想把此次演讲永久保存,如何保存到计算机?
[答:] 请在以下网站选择"已存档的在线座谈" 的 "飞思卡尔的电场感应技术揭秘及其应用在线座谈", 您便可回放在线座谈: http://seminar.chinaecnet.com/seminar/cn/seminarclear.asp
[问:] 我也没来得及看讲解, 你说可以下载, 请提供一下地址, 从哪下载?
[答:] 请在以下网站选择"已存档的在线座谈" 的 "飞思卡尔的电场感应技术揭秘及其应用在线座谈", 您便可回放在线座谈: http://seminar.chinaecnet.com/seminar/cn/seminarclear.asp
[问:] 演讲稿能放在论坛里下载么?谢谢
[答:] 请在以下网站选择"已存档的在线座谈" 的 "飞思卡尔的电场感应技术揭秘及其应用在线座谈", 您便可回放在线座谈: http://seminar.chinaecnet.com/seminar/cn/seminarclear.asp
[问:] 有中文资料吗?有典型应用案例吗?
[答:] 目前没有太多的中文材料。 但是本次网上讨论的材料有中文和英文两个版本。 您可以下载您需要的。 典型的应用案例在我们的讨论中介绍了。 请和我们当地的技术服务联系或和我们的代理商联系获得更多的信息。
[问:] 在液位检测中是否可以消除因泡沫而引起的“假液位”?
[答:] 您的问题实际上包含了对“泡沫液体”和“液体”本身的检测,由于“泡沫液体”的介电常数可能和液体本身的介电常数有较大差别,所以,您在检测这样的液位时,可能会产生一些影响,这时需要您进行大量的数据采集和比较来达到消除“假液位”的影响。
  关于飞思卡尔  

飞思卡尔半导体(NYSE:FSL)是嵌入式处理解决方案的全球领导者,提供业界领先的产品,不断提升汽车、消费电子、工业和网络市场。我们的技术从微处理器和微控制器到传感器、模拟集成电路和连接,它们是我们不断创新的基础,也使我们的世界更环保、更安全、更健康以及连接更紧密。我们的一些主要应用和终端市场包括汽车安全、混合动力和全电动汽车、下一代无线基础设施、智能能源管理、便携式医疗器件、消费电器以及智能移动器件等。公司总部位于德克萨斯州奥斯汀市,在全世界拥有多家设计、研发、制造和销售机构。