Communication between the control system and the sensor utilizes RS232. The control application will be written in C#, therefore additional code will need to sit between the managed C# and the serial hardware access provided by the operating system.

• .NET 2.0 SerialPort Class - "Use this class to control a serial port file resource. This class provides synchronous and event-driven I/O, access to pin and break states, and access to serial driver properties. Additionally, the functionality of this class can be wrapped in an internal Stream object, accessible through the BaseStream property, and passed to classes that wrap or use streams." This would explain why maintenance on the other serial libraries stopped in 2005. Unless serious issues dictate otherwise, I will be using this. ($Free)
  
• SerialPort .Net Reference Article - "This article is about communicating through the PC's Serial COM RS-232 port using Microsoft .NET 2.0 or later by using the System.IO.Ports.SerialPort class."

• ActiveXperts ActiveComport - "ActiveComport is a COM component, that provides an easy-to-use scripting interface for serial, asynchronous communications through a serial port. ActiveComport can control modems, ISDN modems, USB serial devices and other devices and machines that have a serial interface." ($260-$1200)
  
• Windows Serial Component Library - "The Windows Standard Serial Communications Library (WSC) series of software development tools consist of both Win16 and Win32 Dynamic Link Libraries (DLL's) that are based on the Windows serial comm API. The Windows Serial Communications Library uses the standard Windows API to communicate with any device connected to a serial port from within an application. The component library includes 32 functions plus modem control, XMODEM and YMODEM,ASCII and ANSI terminal emulation." Doesn't appear to be a C# library, though their website is confusing. Unmanaged libraries can still be called from C#, it's just more work. ($115)
• WCSC COMM-DRV/Lib.Net - "COMM-DRV/Lib.Net is a professional serial communication library component for the .Net Windows development environment. We understand that your time is valuable and have made this serial communication library/component extremely easy to use. After installing this communication .Net (dotnet) component, you should have a working application in less than 5 minutes. Simply load the C# or Visual Basic .Net example and start working." ($299)
• Franson SerialTools - "Add serial port support to C# or VB.NET Samples and a very straight forward API makes SerialTools simple to use even for a novice programmer." This hasn't been updated since 2005, but that *could* mean it's working really well. ($40-$60)
• SerialPortNet - "SerialPortNet is an open source serial port communication library for Microsoft .NET. It's written in c#, implements complete .NET 2.0 specifications, and is designed to allow for multiple OSes and add-on 3rd party Serial to Network adapters." Project appears to have died but still worth a look. ($OpenSource)