Industrial chillers are commonly used to circulate a constant temperature fluid in a closed loop with liquid cooled instruments and tools in order to increase process repeatability and reproducibility.
循环冷却装置如何维持恒温
The basic components of a chiller consist of a pump to circulate the fluid, a reservoir to hold a volume of cold fluid in the chiller, a refrigeration system to cool the fluid, and a temperature control module. (See Figure 1.)
A standard, off-the-shelf temperature controller can be used as a temperature control module. Controllers are available from any number of manufacturers with a variety of options. All include a temperature display, are panel mounted, and accept temperature inputs from Resistance Temperature Detectors (RTDs) or thermocouples. Various communications options are also available. A helpful feature of many controllers is a Proportional–Integral–Derivative (PID) auto-tune function. This allows the user to let the controller calculate the optimum response to system disturbances. Disturbances come in the form of varying process loads, set point changes, and noise. After auto-tuning is completed, the user may need to make some additional adjustments to the tuning parameters to ensure that the temperature of the process fluid is within the process control limits. This does not necessarily complete the work of tuning the chiller with the tool. The user must be aware that the auto-tune feature will attempt to tune the temperature controller at the one operating point being evaluated.
Process dynamics are often affected by conditions that only exist at certain times or under specific circumstances. If these special conditions can be sensed or predicted in some way, a method of adaptive (feed forward) control is needed to supplement the reactive (feedback) control used in a typical control scheme. Chillers serving applications with these advanced needs are often better suited by the use of Programmable Logic Controllers (PLCs) and Operator Interface Terminals (OITs). (See Figure 2.)
The use of a PLC provides flexibility to satisfy the needs of a more demanding control environment. It allows for the seamless integration of non-process temperature related process measurements such as pressures, flow rates, ambient temperature, etc. or critical events like pump overload, safety shut down, etc. in an adaptive control scheme. PLCs also provide a means of data collection and communication. They are easily connected to host systems via a myriad of communications options.
Various field bus connections are available (Profibus, DeviceNet, Lonworks, etc.) as well as non-proprietary serial and Ethernet links. This allows the user to better integrate the chiller with the tool. While temperature control is a critical function for many industrial processes, temperature stability is critical for some processes as well. Increased stability generally correlates to increased cost.
Many applications require a temperature that is stable to ±0.5°C of a given set point temperature at a specified heat load. This level of stability can be accomplished by measuring the temperature in the reservoir and cycling an on-off valve in the refrigeration system. (See Figure 3.) A basic PID algorithm in the temperature control module cycles the on-off valve as needed. The reservoir provides a volume of constant temperature fluid to help reduce the impact of any small temperature changes due to heat load changes from the tool.
While the reservoir helps maintain a constant temperature for the fluid being supplied to the tool, it also masks large temperature spikes in the fluid returning from the tool. These changes result from varying heat loads. For example, a laser in operation may add a constant 300 W of heat load to the fluid for 5 minutes. The laser power may then run at 500 W for 5 minutes, and then be brought back down to 300 W for another 5 minutes. This cycle may repeat over and over. Increasing the heat load by 67% will suddenly change the fluid temperature returning to the chiller. Since the fluid temperature in the reservoir changes more slowly, the temperature control module is slower to respond to these changes.
Temperature stability can be increased for dynamic processes by measuring the temperature of the fluid at the exit of the refrigeration system and prior to the reservoir. (See Figure 4.) The temperature control module sees the spikes in fluid temperature and can respond accordingly. The temperature stability of the fluid being supplied to the tool can be doubled by simply changing the measurement point. (See Figure 5.)
需要特别注意的是，如果使用开-关阀的冷却装置的设计稳定性为±0.5°C，继续增加稳定性会导致更频繁的循环而降低阀的使用寿命。在成品温度控制器上使用自动调节功能时可能出现这个问题。因此，冷却装置应只提供维持过程受控所需的稳定性。
与冷却装置温度控制相关的另一个常见问题是冷却装置和工具之间的环境温度损失。过程流体温度比室温高太多或低太多而冷却装置与工具之间距离远管道长时，通常会发生这个问题。有时，冷却装置和工具甚至不在同一层楼。例如，由于室温会增加液体温度，冷却装置出口温度为15°C的液体到达工具时温度可能上升到20°C。过程要求供应给工具的液体温度为恒定的15°C，而不是20°C。对于这个问题，可以在5°C的温度控制模块中输入偏差。为冷却装置输入15°C 的设定点温度，但冷却装置的实际控制温度将达到10°C。过程将获得所需的15°C液体，而冷却装置将通过显示屏或通信传达15°C温度值。
一些过程对温度更敏感，如医疗设备、特定激光器和半导体设备所用的过程。对于循环冷却装置，在指定热负荷条件下特定设定点温度±0.1°C的稳定性很常见。但如上所述，建议您确保这个稳定性水平确是给定过程所需，因为这可能导致冷却装置组件或开发成本增加。温度控制模块中的PID算法将控制制冷系统中的开-关阀或调节阀。调节阀通常为一个步进阀，提供对运行点更精细的控制。与开-关阀一样，阀体使用寿命期间也没有特定的循环次数限制。与开-关阀相比，调节阀完全打开和关闭所需时间更长。因此，如果设定点出现阶跃变化，冷却装置需要更长时间渐变至新温度。
控制多个液体回路或在热负荷高度可变的大温度范围内运行时，冷却装置中的温度控制可能非常复杂。在这种情况下，可以使用PLC和OIT，因为它们可经过编程控制多个控制设备并拥有多个PID回路。由于仅受针对其创建的程序的限制，这些设备可以提供最大的灵活性。
总之，谨慎确定系统运行点和所需稳定性至关重要。错误指定这些项目可能导致工具温度失控和/或不必要的成本增加。经验丰富的冷却装置制造商可以根据正确的输入提供正确的定制或标准冷却器选择。
让RS232通信为您所用
未来的客户满意度要求更加严格。客户要求服务与其组织无缝连接，成为组织的一部分。冷却系统及循环冷却装置本质上是通过内部传感器及控制来测量整个系统状态的关键信息。因此，冷却系统和冷却装置可通过RS232界面有效地进行系统问题通信。这些重要信息有助于维持和保护整个系统中的设备。
最简单的RS232可用于控制基本冷却装置功能并检查系统是否存在故障。大多数人仅将RS232用于开启/关闭设备及控制基本功能，例如设定点。然而，由于冷却装置的几乎所有功能都可以通过RS232界面使用，因此其功能远不止这些。
控制多个液体回路或在热负荷高度可变的大温度范围内运行时，冷却装置中的温度控制可能非常复杂。在这种情况下，可以使用PLC和OIT，因为它们可经过编程控制多个控制设备并拥有多个PID回路。由于仅受针对其创建的程序的限制，这些设备可以提供最大的灵活性。
总之，谨慎确定系统运行点和所需稳定性至关重要。错误指定这些项目可能导致工具温度失控和/或不必要的成本增加。经验丰富的冷却装置制造商可以根据正确的输入提供正确的定制或标准冷却器选择。
例如，Boyd循环冷却装置可以进行压力变化监控和通信。系统安装并投入运行后，可获取液体侧当前压力读数并用作参照点，以持续监控液体侧压力。如果您的设备在一段时间或几天内突然出现压力上升或下降趋势（比如由于管道系统故障、腐蚀或过滤器堵塞原因），则您将在潜在问题出现前收到警告。
缓慢而稳定的温度变化也是即将出现问题的指标。如果系统在正常运行中缓慢失去维持温度的能力，可能意味着被冷却的电子部件由于内部故障而发生过热或不工作，或者冷却装置正在丧失性能。Boyd冷却装置能够测量低至1/100度的温度变化并通过RS232界面进行通信。
启动系统测试开发，或使用冷却装置测量和控制功能定期运行的测试都是在问题出现并导致停工前确定问题的非常有效的方式。使用冷却装置内部传感器和RS232界面测量温度、压力和其他参数，可避免集成额外的温度和压力传感器而产生的支出和复杂性，而尽早诊断并修复故障或系统问题也可节约成本并缩短停工时间。
下载RS232通信软件 并拷贝至您的硬盘。解压到单个文件夹（如桌面）；请勿解压KodiakPCHost.cab文件。由于防火墙的原因，请将setup.exr重命名为setup.exe。运行setup.exe文件。如果弹出窗口信息显示您系统中存在比正在安装的文件版本更新的文件，请选择保持最新文件。然后，确保您的com 1接口设置为9600波特、8数据位、1停止位、无校验。也不应有软件流控制。请注意，如果使用WinZip解压压缩文件，版本应至少为9.0。该程序是反映主屏幕和控制的简单界面。您您必须关闭弹出窗口拦截程序才能进行下载。
Learn more about Recirculating Chillers where can implement intelligent system controls like RS323 Communications.
