在线咨询买家必读:
一、店铺所有价格均不是实价，如需了解产品价格，请联系在线客服。
二、现货付款当日发货；期货从付款日起开始计算时间，货期不含国内外节假日。
三、买家通过快递或物流签收货物后，若有异议，请在收到货物当天内提出。
1、下单前，买家需向卖家确认价格和货期；若买家单方面下单，则订单视为无效；
2、下单后,买家不得更改产品品牌，规格型号以及数量、单价等，因买家提供产品规格型号错误而造成错误订货的，卖家不负责更换货品、退货、退款等，也不承担因此造成的损失；
3、下单后，若无质量问题，不接受无理由退/换货、退款;
4、因此产品生产厂家停产、升级无3C、涨价、受限制造成无法订货，则订单取消，卖家不承担任何相关法律责任；
5、因自然天气、运输货运、政法政治原因等非卖方所能控制之客观因素导致货期延误，卖家不承担任何相关法律责任，由买卖双方协商订单是否依旧生效。
请各位买家知悉相关条款，如有异议，请咨询解决相关疑问！
In terms of database:
DCS generally provides a unified database. In DCS system, once a data exists in the database, it can be referenced in any case. The database of PLC system is usually not unified. Configuration software, monitoring software and even filing software have their own database. In terms of time scheduling:
Generally, the program of PLC cannot run according to the preset cycle. PLC program is executed from beginning to end and then from the beginning（ Now some new PLCs have been improved, but the number of task cycles is still limited.
DCs can set the task cycle. For example, fast task, the same is sensor sampling. The change time of pressure sensor is very short, and it can use 200ms task cycle for sampling, while the lag time of temperature sensor is very large, and it can use 2S task cycle for sampling. In this way, DCs can reasonably schedule the resources of the controller.
In terms of network structure:
Generally speaking, DCS usually uses two-tier network structure, one is process level network. Most DCS use their own bus protocols, which are based on standard Huai serial port transmission protocol RS232 or RS485. The second layer is the operation level network, which adopts the network standard of moderate data throughput, fast transmission speed and convenient connection. Because the operation level network is generally arranged in the control room, the requirement of anti-interference is relatively low, and Ethernet is the best choice.
The task of PLC is relatively simple, the amount of data to be transmitted is generally not too large, so the common PLC system is a layer of network structure. Either the process level network and the operation level network are combined together, or the process level network is simplified as the internal connection between modules, and PLC will not or rarely use Ethernet. In terms of application objects:
PLC is generally used in small automatic control places, such as equipment control or a small amount of analog control and interlocking, while large-scale applications are generally DCS. Of course, this concept is not very accurate, but it&＃39;s very intuitive. It&＃39;s customary to call a system larger than 600 points as DCS and a system smaller than 600 points as PLC.
