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HPFM - High Pressure Flow Meter

The High Pressure Flow Meter (HPFM) is designed to perform quantitative root and stem analysis without having to dig up roots or drag limbs back to the lab. In most cases, the analysis of a sample root or shoot is completed in as little as 10 minutes. You can quickly measure the major components of the hydraulic conductance in the soil-plant-atmosphere continuum (reference # 70). The hydraulic architecture of a whole shoot or of a single leaf can be represented by a resistance diagram similar to the one on the left. One can measure the values of the individual hydraulic resistances, then compute the pattern of water flow and water potentials in the resistance network. Each hydraulic resistance element (R) equals the pressure difference driving flow through the element divided by the resulting flow (F) (reference # 82). In the HPFM method, the resistance of the root and shoot are measured separately by pressure perfusion and added together. The HPFM will help plant physiologists and agronomists look forward to those seasonal studies of root and shoot progression, water potential, or soil treatment effects.

The HPFM is designed for two types of numerical analysis The first analysis is an in-situ transient analysis of hydraulic conductance. HPFM measures the flow as the water pressure increases while flowing into the root or shoot. The software then intelligently calculates the slope of the increased flow and pressure. That slope is the hydraulic conductance. The second analysis is a quasi-steady state, constant pressure and flow into the sample. This derives the flow pressure and conductance in a steady state environment.

Software

The HPFM comes with menu-driven software that is easy to use and straightforward in it's approach. The software also includes diagnostics and calibration modes to assure the user of correct readings. All data is saved to the PC hard drive for later analysis by your favorite spreadsheet and graphing packages.

To run this software you need an IBM compatible computer with an 800 x 600 pixel screen or better. The computer must be running on Microsoft Windows 95 or 98 and it must have a parallel printer port. The program will not work with Windows NT or 2000. If you wish to perform your own calibrations, the computer will also need an unused RS232 serial port but we recommend that all calibrations be done by Dynamax. We suggest that you use a notebook or sub-notebook computer with the HPFM, especially if you plan to use the system in the field.

HPFM Measurements

Transient

The transient measurement of conductance of your root or shoot sample allows a quick and fast way to gather data in the field or the lab. Acquiring the data quickly is important when dealing with root systems. The root systems as well as the shoots of many plant species have the ability to "repair" themselves and plug off the xylem. Also, there is an osmotic effect in root systems that will increase the pressure (and therefore reduce the flow) as more water is injected into the root system.

Regression

While measurement of the Transient is simply graphing a line of increasing pressure and flow, Regression is the ̴̣best fit" of that graphical line and calculating the slope. That slope is the hydraulic conductance of the measured plant. Set Zero - Steady State The "SetZero" option allows you to measure and record the mismatch so that flow measurements can be corrected between pressure sensors to improve the accuracy of measurements. This option will also allow you to do a pressurization of the HPFM with the outlet valve closed and the highest flow range selected.

Flow Meter

Quasi-steady state flow meter measurements are usually done on whole shoots because flow can be approximately constant with constant applied pressure. The resistances are reported rather than conductance because one of the common aims with quasi-steady state measurements is to measure the resistance of the whole shoot and its components, e.g., leaf blades, petioles, small stems, large stems etc.

Calibration

Dynamax will supply the HPFM with a professional factory calibration. The calibration file is on the CD-ROM that comes with the HPFM If you wish to perform a custom calibration on the HPFM, you are required to have an Electronic Balance with a 4 decimal place resolutions and RS232 communication facility.

Couplings

Dynamax includes all the fittings and couplings you may require for analysis. These additional parts include high quality couplings machined out of Lexan for durability and easy viewing.

Compression couplings to plants

HPFM-XP versus HPFM-C

The HPFM-XP model is designed to perform analysis on small plants with stems measuring between 1-36mm in diameter. Due to a reduced CAT capacity it is only possible to operate the system over the first 4 flow ranges hence the Grey High Flow range has been removed and the brown range is used for calibration purposes only. The HPFM-XP incorporates a smaller capacity Air Supply Tank into the system to allow greater ease of operation and convenience in the field. By comparision the larger CAT and Air Supply Tank supplied with the HPFM-C make this unit a more suitable option for larger stems upto 55mm in diameter and high volume measurements in a lab.