The float sinks to the bottom of the headspace vapor and floats on top of the process fluid. The down side is the possibility of glass breakage resulting in spills or safety to personnel.įloats work on simple principle of placing a buoyant object with a specific gravity intermediate between those of the process fluid and the headspace vapor into the tank, then attaching a mechanical device to read out its position. The benefit of this design is the ability to the see the true level through the clear glass. Some of these technologies can be used for multilevel applications where two or more immiscible fluids share a vessel.Īvailable in a variety of designs, both armored and unprotected, glass gauges have been used for over 200 years as a simple method to measure liquid level. We will assume also that there is only one, uniform, process fluid in the tank. Throughout this article we assume the density of the vapor in the headspace (typically air) to be negligible compared with that of the process fluid. Combining this requirement with the need for advanced communication capabilities and digital calibration schemes explains the trend toward embedding microprocessor-based computers in virtually all level measurement products (see Figure 1). New wireless capabilities can be found in the latest transmitters’ signals, allowing them to be sent over tremendous distances with virtually no degradation.Īs for the more advanced measurement technologies (e.g., ultrasonic, radar and laser), the more sophisticated digital encoding formats require digital computer intelligence to format the codes. Digital signals coded in any of a number of protocols (e.g., Foundation Fieldbus, Hart, Honeywell DE, Profibus, and RS-232) are the most robust, but the older technologies such as RS-232 can handle only limited distances. Current loops can carry signals over longer distances with less degradation. The simplest and oldest industrial signal communication is 4-20 mA current loops (where the loop current varies with the level measurement) are the most common output mechanism today. Analog voltages are simple to setup and deal with, but may have serious noise and interference issues. Useful transducer output signal formats for computer automation are current loops, analog voltages and digital signals. This requires sending data in a machine-readable format from the sensor to the control or monitoring system. When more complex physical principles are involved, emerging technologies often use computers to perform the calculations.
Hydrostatic head measurements have also been widely used to infer level. A simple float having a specific gravity between those of the process fluid and the headspace vapor will float at the surface, accurately following its rises and falls. Other level-detection devices include those based on specific gravity, the physical property most commonly used to sense the level surface. They are therefore being rapidly replaced by more advanced technologies. It can be stated without reservation that conventional sight glasses are the weakest link of any installation.
Seals are prone to leak, and buildup, if present, obscures the visible level. The material used for its transparency can suffer catastrophic failure, with ensuing environmental insult, hazardous conditions for personnel, and/or fire and explosion.
#Type measurement pica point measure depth of column manual
A manual approach to measurement, sight glasses have always had a number of limitations. The simplest and oldest industrial level measurement device is, of course, the sight glass.
0 kommentar(er)
