83SR04E-E GJR2390200R1210 ABB

Analog quantity refers to some continuously changing physical quantities,such as voltage,current,pressure,speed,flow and so on.

PLC is developed after the introduction of micro-processing technology from relay control,and can be used for switch quantity control conveniently and reliably.Since the analog quantity can be converted into a digital quantity,the digital quantity is only a multi-digit switch quantity,so the converted analog quantity can also be processed and controlled by the PLC completely and reliably.

Because continuous production processes often have analog quantities,analog quantity control is sometimes called process control.

Most of the analog quantities are non-electricity quantities,while PLCs can only handle digital quantities and quantities of electricity.All the conversions between them must be realized by sensors,which convert analog quantities into digital power.If this power is not standard,it must go through the transmitter to turn the non-standard power into a standard electrical signal,such as 4-20mA,1-5V,0-10V and so on.

At the same time,there is also an analog input unit(A/D)to convert these standard electrical signals into digital signals;an analog output unit(D/A)to convert the digital quantity processed by the PLC into an analog quantity-standard electrical signal.

模拟量是指一些连续变化的物理量，如电压、电流、压力、速度、流量等。

PLC是由继电控制引入微处理技术后发展而来的，可方便及可靠地用于开关量控制。由于模拟量可转换成数字量，数字量只是多位的开关量，故经转换后的模拟量，PLC也完全可以可靠的进行处理控制。

由于连续的生产过程常有模拟量，所以模拟量控制有时也称过程控制。

模拟量多是非电量，而PLC只能处理数字量、电量。所有要实现它们之间的转换要有传感器，把模拟量转换成数电量。如果这一电量不是标准的，还要经过变送器，把非标准的电量变成标准的电信号，如4—20mA、1—5V、0—10V等等。

同时还要有模拟量输入单元(A/D)，把这些标准的电信号变换成数字信号；模拟量输出单元(D/A)，以把PLC处理后的数字量变换成模拟量——标准的电信号。