高性能电磁流量之恒流源的设计.docxVIP

高性能/电磁流量计之恒流源的设计（一）浙江迪元/电磁流量计（/YYD电磁流量计）是一种根据法拉第电磁感应定律来测量管内导电介质体积流量的感应式仪表，采用单片机嵌入式技术，实现了数字励磁。技术水平处于国内领先地位。?/YYD电磁流量计因其有测量精度高、管道流阻小（几乎为零）、测量范围广（能测低导电液体的流量），使其有广泛的用途，在满足现场监测显示的同时可输出标准直流电流信号(4～20mA)、频率信号、485通讯、HART通讯等，供记录、调节、控制用，广泛应用于化工、电力、环保、轻纺、冶金、矿山、医药、造纸、给排水、食品、制糖、酿造等工业技术和管理部门。根据法拉利原理，/电磁流量计的传感器里必需要有一对磁场，这一对磁场不像发电机一样用一对磁铁产生，而是通过一对线圈（线圈中间有一打铁氧体的磁芯）通电产生，通常我们称之为励磁。为了使这一对线圈产生一个恒定的磁场，我们必需要使用恒流源。那么恒流源是如何产生的呢？较早的/电磁流量计的恒流源是用4DH7恒流管产生的，在维修/电磁流量计的工作中，我们经常偶到仪表的恒流源损坏，原因是4DH7的质量不够好。我们有没有更好的解决办法呢？答案是肯定的，下面我就介绍一种恒流源——基于LM317的恒流源。LM317是一种可调的三端稳压源，设计输出电流可达1A，输出电压范围为1.3~37V。其封装方式有SOT-223、D-PACK、TO-220和D2-PACK，如下图：LM317的主要特性是：1、输出可调电压1.3V~37V；2、输出电流达1A；3、内置短路保护；4、内置高温保护；5、输出补偿；6、符合RoHS标准7、内置1.25V基准电压等。LM317的引脚特点如下图所示：LM317组成的恒流源结构很简单，只要外部连接一只电阻，就可以设计成你所需要的各种电流，基本电路图如下：由于LM317内部有一1.25V的基准电压，所以V（OUTPUT-ADJ）=1.25V，磁场强度（k为比率系数、μ0为真空磁导率、N为线圈匝数、I为流过线圈的电流大小）。由以上条件，/电磁流量计的传感器的磁场强度就可以近似的计算了。the old party and the difficulties of the masses. In the mass line of educational practice, the old party members, five households, orphans, households and households are not included in the low range of focus on helping object, clear each party members and cadres at least helping needy families, the annual visits to comfort Ask the supporting object of not less than 2 times the target. 4, at least one run Huimin practical. According tothe old party and the difficulties of the masses. In the mass line of educational practice, the old party members, five households, orphans, households and households are not included in the low range of focus on helping object, clear each party members and cadres at least helping needy families, the annual visits to comfort Ask the supporting object of not less than 2 times the target. 4, at least one run Huimin practical. According tothe old party and the difficulties of the masses. In the mass line of educational practice, the old party members, five households, orphans, households and households are not included in the low range of focus on helping object, clear each par