为了控制张力，需要构成张力控制系统。因为张力只能在两个（或两个以上）具有驱动（或制动）力矩的工艺设备间形成， 所以张力控制系统是在两个传动控制系统基础上构成的。其中一个传动控制系统作为张力控制系统的速度基准，称为速度基准系统，而另一个传动控制系统按张力要求建立负载，形成张力，实质是对速度基准系统按要求张力进行速度跟随， 称为张力可控的速度跟随系统。张力控制的任务一般多放在后一系统上， 所以人们习惯地只将后者称为张力控制系统。

张力控制系统由于应用场合、设备、构成原理不同而多种多样。但按结构形式、控制原理可大致将其归纳为直接张力控制系统、间接张力控制系统、活套张力控制系统三大类。

通过张力检测环节 （张力检测传感器）实现对张力的闭环反馈控制的系统。卷取机和轧机机架间的直接张力控制系统分别如图1 （a）、（b） 所示。

实现直接张力控制，首先要有张力检测传感器（张力计）。它被装在张力测量机构的张力辊下（见图1）。张力计实为压力计，现用的压力计有压磁式、感应式、电阻应变片式等多种型式。

直接张力控制大多用于张力调节范围大， 精度要求高及易于安装张力计的场合， 或在无法构成间接张力控制系统时使用。

有时为了提高张力调节动态及静态性能， 扩大张力调节范围，用间接张力控制实现粗调，起扰动补偿作用，用直接张力控制实现精调，两者合在一起构成张力复合控制。

直接张力控制和张力复合控制多应用于带材、箔材冷轧机或连续加工线的卷取机或其机架间、加工设备间的张力控制上。Tension control The technique of automatically controlling the tension of a processed material in continuous motion or at rest between two processing devices. In a variety of continuous production lines, a variety of strips, wires, profiles and their reproducts, in rolling, drawing, embossing, coating, printing, cleaning and winding processes often need to be controlled tension. The tension control can be constant tension control or variable tension control. Variable tension control refers to the tension according to a predetermined law, or according to the process needs to change at any time, or as a parameter of the automatic control system to participate in the adjustment of the tension control technology.

In order to control the tension, it is necessary to construct a tension control system. Because tension can only be formed between two (or more) process equipment with driving (or braking) torques, the tension control system is constructed on the basis of two drive control systems. One of the transmission control system as the speed reference of the tension control system, called the speed reference system, and the other transmission control system according to the tension requirements to establish the load, the formation of tension, in essence, the speed of the speed reference system according to the required tension to follow the speed, called the tension controllable speed following system. The task of tension control is generally placed on the latter system, so people are accustomed to only referring to the latter as the tension control system.
Tension control systems are varied due to different applications, equipment and composition principles. However, according to the structure and control principle, it can be roughly summarized into three categories: direct tension control system, indirect tension control system and looper tension control system.
Direct tension control system
The system realizes the closed-loop feedback control of tension through the tension detection link (tension detection sensor). The direct tension control system between coiler and mill stands is shown in Figure 1 (a) and (b) respectively.
To achieve direct tension control, you must first have a tension detection sensor (tensiometer). It is mounted under the tension roll of the tension measuring mechanism (see Figure 1). The tensiometer is actually a pressure gauge, and there are many types of pressure gauges in use, such as piezomagnetic type, induction type, resistance strain gauge type, etc.
Direct tension control is mostly used in situations where the tension adjustment range is large, the accuracy is high and the tensiometer is easy to install, or when an indirect tension control system cannot be formed.
Sometimes, in order to improve the dynamic and static performance of tension regulation and expand the range of tension regulation, indirect tension control is used to achieve rough adjustment, play the role of disturbance compensation, and direct tension control is used to achieve fine adjustment.
Direct tension control and tension compound control are mainly applied to the tension control of strip and foil cold rolling machine or coiler of continuous processing line or between its frame and processing equipment.