Orifice Flow vs PIDTune

Measurement of fluid flow in pipes and conduits using orifice plates are very common in industrial applications. This app quickly computes the flow rates for liquid and gases based on standard parameters as per the model shown. Users can pick any fluid from a list of fifteen most common fluids used in industrial applications. Therefore, this app can be a very helpful tool for practicing engineers and designers in design and analysis of flows in different applications. A case study on CO2 flow rate is shown in the screen shot. The result is consistent with other methods used by the industry in computation and difference is less than 0.1%. Fluids that are not in the list, users can create a custom fluid with property data and compute the flow rate using the model provided in this app. Custom fluid data can be saved and reloaded every time when custom fluid is selected. Fluids: Air, Steam, Water, Nitrogen, Oxygen, Hydrogen, Helium, CO2, Methane, Ethane, Chlorine, Ammonia, Argon, Hydraulic oil, HFC(R410A), Custom (user's choice). Orifice Type: App gives four different standard orifice design with recommended discharge coefficients as shown in the following screen shot. It also provides the details of the model used in the computation of flow rates for liquid and gases. This model is valid even for nozzles, venturi-flow meters for which the discharge coefficient (Cd) is unity. Measuring Parameters: Fluid inlet temperature and pressure, orifice geometry, pressure differential using standard pressure taps (ISO 5167), are the standard parameters required in the computation. Based on the orifice geometry, recommended discharge coefficient Cd is used. However, users can edit this using manufacturer’s data for more accurate results. App notes provides brief description of different orifice parameters for quick reference. Unit of Measurement: Users can choose different unit of measurement for both flow as well as pressure drop under given unit standard (SI or USCS). This can be conveniently selected while choosing the fluid from the picker list. App notes provides additional guideline with a link for complete documentation on implementation and validation of math-models used with industry examples.

PID Tuner uses the IMC (Internal Model Control) method to calculate PID tuning parameters. I’ve tried a lot of tuning methods over the years and have found this one to be the best. The app is written for the iPad to show all the information on one page. The program calculates: PID Parameters: Controller Gain (Kc) Integral Time (Ti) Derivative Time (Td) For process types First Order with Dead Time (FO) Second Order with Dead Time (SO) Integrating or Long Time Constant with Dead Time (I) For controller types Parallel (non-interacting) c(s) = Kc (1 + 1/(Ti s) + Td s) Series (interacting) c(s) = Kc (Ti s + 1)/(Ti s)(Td s + 1) For controller modes PID PI You can either enter the process gain (Kp) directly or enter the changes in the controlled virable (CV) and manipulated variable (MV). Tuning aggression is adjusted using the slider to set the closed loop time constant to the process time constant ratio (λ/Ƭ). The closed loop time constant (λ) is the time the controller is expected to reach set point (plus the dead time (ϴ)). Setting the closed loop time constant to process time constant ratio (λ/Ƭ) to 1.0 will make the MV change to its final value and allow the process to settle out to the setpoint. Setting (λ/Ƭ) greater than 1.0 will give a slower responce. Setting (λ/Ƭ) less than 1.0 will cause the MV to make a larger change and then reduce to its final value. Tight tuning would be to set the close loop time constant to the dead time. Use the Integrating Process type (Ƭ = ∞) for both integrating processes or processes with long time constants. These processes use the maximum slope as the process gain. Tuning aggression for these processes is determined by setting the closed loop time constant to the dead time ratio (λ/ϴ). Once again, setting the closed loop time constat to the dead time gives tight control. References: “Probably the test simple PID tuning rules in the World,” Sigurd Skogestad, Jounal of Process Control, July 3, 2001 “Consider the generalized IMC-PID method for PID controller tuning of time-delay processes,” Y. Lee, S. Park, M. Lee, Hydrocarbon Processing, January 2006