The Need for Digital Mass Flow Controllers In The IIoT
Digital Mass Flow Controllers for gases are becoming standard equipment for bioreactors and fermenters. In the case of process development and scale-up, accurate and precise control and measurement of gas flow is a requirement. Many bioreactor vendors still communicate with gas flow controllers through analog signals; either 4-20 mA or 0-5/10 volt. This is an outdated approach, especially as the Industrial Internet of Things (IIoT) has become a more viable and valuable approach to the integration of instruments and control elements. One of the connected elements we rely on is the Alicat Mass Flow Controller.
If you are new to the concept of the Internet of Things, start here: http://www.wired.com/insights/2014/11/the-internet-of-things-bigger/.
Most modern gas flow controllers now contain a microprocessor and can communicate through digital protocols. Instead of a single analog data line controlling a single controller, we now communicate with Modbus RTU through a serial RS485 port to talk to multiple mass flow controllers.
Digital communication allows for faster and better data transfer. A set point of, say 4.3, in the microprocessor is a digital value that can be set and maintained by a digital gas flow controller. Old style 4-20 mA communication requires that the 4.3 value be turned into an analog approximation of that value. Every time that occurs, data integrity is reduced.
Why We Recommend The Alicat Mass Flow Controller
Digital communication provides for a broader range of data as well. For example, Alicat Scientific provides a lot of flexibility with adjustments for the following:
- Mass flow
- Volume flow
- Temperature
- Pressure
- A gas totalizer
These devices have calibration settings based on the gas type, which allows users to access advanced features such as zero or tare and changing the gas type measured.
Another big benefit of going digital is the ability to easily add or swap gas flow controllers. Modbus allows users to address the specific devices so users can add additional gas flow controllers without much hassle. For example, ILS had a customer which required 6 gas flow controllers per reactor. Adding additional gas flow controllers requires a simple cable. No additional boards or components were added to the reactor controller.
When selecting mass flow controllers, you need to pay attention to how gas range and the controller’s precision affect low flow. This is especially true if you are choosing an O2 controller. The larger the range, the larger the minimum flow. For example, an Alicat mass flow controller has a low end flow that is 0.5% of the range. So a 1000 sccm mass flow controller will have a smallest possible flow of 0.5 sccm.
Supporting Multiple Reactor Sizes
In some cases, it is desirable to connect both a small and a large flow O2 controller to create a system that supports multiple reactor sizes. This allows our customers to use the same reactor controller and maintain fine control of gas flow when switching between a 3-liter reactor and a 15-liter reactor. Modbus makes this an easy problem to solve by handling multiple controllers.
