PMR-5 STEADY STATE POROMETER OPERATOR'S MANUAL Version · PDF filePMR-5 STEADY STATE POROMETER OPERATOR'S MANUAL Version 5.02 © 2006 PP Systems. All Rights Reserved 17 October...

PMR-5 STEADY STATE POROMETER

OPERATOR'S MANUAL

Version 5.02

© 2006 PP Systems. All Rights Reserved

17 October 2006

Europe North America PP Systems PP Systems Inc.

Unit 2, Glovers Court, Bury Mead Road. 110 Haverhill Road, Suite 301 Hitchin, Hertfordshire, SG5 1RT, U.K. Amesbury, MA 01913 U.S.A.

Tel: +44 1 462 453 411 Tel: +1 978 834-0505 Fax: +44 1 462 431 090 Fax: +1 978 834-0545

Email: [email protected]

Web Site: http://www.ppsystems.com

Table of Contents

Table of Contents

Table of Contents...........................................................................................2

Preface............................................................................................................3 Notice............................................................................................................3 Documentation Conventions.........................................................................3 User Registration ..........................................................................................3 Service & Warranty .......................................................................................4 Contact Information.......................................................................................4 Unpacking Your Equipment ..........................................................................4

Introduction....................................................................................................5

Technical Specifications ...............................................................................5 EGM-4 Environmental Gas Monitor ..............................................................5 PMR-5 Steady State Porometer....................................................................5 Cuvette .........................................................................................................5 Integral Air Supply Unit .................................................................................6

Porometer Layout ..........................................................................................7 FIGURE 1 VIEW OF PMR FROM LEFT HAND SIDE.................................7 FIGURE 2 VIEW OF PMR FROM RIGHT HAND SIDE .............................8 FIGURE 3 VIEW OF PMR FROM TOP .....................................................9 FIGURE 4 ELECTRICAL CONNECTIONS TO THE EGM.......................10

Use as a Porometer .....................................................................................10 Operation ....................................................................................................10 Adjustment and Selection of Flow and Humidity .........................................11 Power On....................................................................................................12 Main Menu ..................................................................................................12 SET Menu...................................................................................................13 REC Menu ..................................................................................................13

Porometer Display 1 (Serial Number input) ..................................................................... 15 Porometer Display 2 (Rb/Area setting) ............................................................................ 15 Porometer Display 3 (selection of Light Type to set TRANS) .......................................... 15 Porometer Display 4 (Sensor Balance)............................................................................ 16 Porometer Display 5 (Record and Plot Number).............................................................. 16 Porometer Display 6 (Measurement Display/Record)...................................................... 17 Porometer Display 7 ( CO2 Concentration and Atmospheric Pressure) .......................... 19

Calculations .................................................................................................20

RS232 Data Transfer....................................................................................23 Record Structure.........................................................................................23

Daily Checks ................................................................................................24

Storage .........................................................................................................24

Calibration ....................................................................................................25

Maintenance .................................................................................................25

Diagnostics ..................................................................................................26

PMR-5 Steady State Porometer – Version 5.02 - 2 -

Preface

Preface

Notice This equipment must not be used in situations where its failure could result in injury or death.

For applications where failure of this equipment to function correctly would lead to consequential damage, the equipment

must be checked for correct operation and calibration at intervals appropriate to the criticality of the situation.

PP Systems' equipment warranty is limited to replacement of defective components, and does not cover injury to persons or property or other consequential damage. This manual is provided to help you install and operate the equipment. Every effort has been made to ensure that the information contained in this manual is accurate and complete. PP Systems does not accept any liability for losses or damages resulting from the use of this information. It is extremely important that you take the time to review this Operator’s Manual prior to installation and operation of the equipment. Otherwise, damage may be caused which is not covered under our normal warranty policy. This manual, and the information contained in it, is copyright to PP Systems. No part of the manual may be copied, stored, transmitted or reproduced in any way or by any means including, but not limited to, photocopying, photography, magnetic or other mechanical or electrical means, without the prior written consent of PP Systems. Windows and Excel are registered trademarks of Microsoft. Quattro Pro is a registered trademark of Borland Lotus 1-2-3 is a registered trademark of Lotus. MS-DOS is a registered trademark of IBM.

Documentation Conventions If viewed electronically, text marked blue act as Hyperlinks. Some links refer to links to external files, which may cause the viewer to prompt whether the action should be performed.

User Registration It is very important that all new customers register with us, to ensure that our user list is kept up to date. If you use any of PP Systems products then please register yourself electronically on our web site at:

http://www.ppsystems.com/Register.html Only REGISTERED users will be allowed access to our protected “Users” section of our web site. This section will contain important product information including hardware/software updates, application notes, newsletters, etc.

Thank you in advance for your co-operation.


Preface

Service & Warranty PP Systems' equipment warranty is limited to replacement of defective components, and does not cover injury to persons or property or other consequential damage. The equipment is covered under warranty for one complete year, parts and labour included. This, of course, is provided that the equipment is properly installed, operated and maintained in accordance with written instructions (i.e. Operator's Manual). The warranty excludes all defects in equipment caused by incorrect installation, operation or maintenance, misuse, alteration, and/or accident. If for some reason, a fault is covered under warranty, it is the

responsibility of the customer to return the goods to PP Systems or an authorized agent for repair or replacement of

the defective part(s).

Contact Information

Europe USA & Canada PP Systems PP Systems, Inc. Unit 2, Glovers Court, Bury Mead Rd. 110 Haverhill Rd, Suite 301 Hitchin, Herts SG5 1RT Amesbury, MA 01913 UK USA Tel: #44-1462-453411 Tel: #1-978-834-0505 Fax: #44-1462-431090 Fax: #1-978-834-0545

e-mail: [email protected]

Unpacking Your Equipment It is extremely important that you check the contents of your equipment immediately upon receipt to ensure that your order is complete and that it has arrived safely. Please refer to the checklist supplied (if applicable) for a detailed list of spares and accessories that are included with your order.

DO NOT DISCARD ANY OF THE PACKAGING MATERIAL UNTIL ALL OF THE ITEMS LISTED ARE ACCOUNTED FOR.

WE RECOMMEND THAT YOU RETAIN THE ORIGINAL PACKING FOR FUTURE USE.

If you suspect that any of the items listed on the appropriate checklist are not included or damaged, you must contact PP Systems or authorised distributor immediately.


Introduction

Introduction The PMR-5 is a porometer that is designed to work only with PP SYSTEMS EGM-4 IRGA.. The EGM-4 supplies the electrical power, measures the outputs from the porometer sensors, processes the results and then displays and records the data. Existing EGM-4 units require a small modification to fit the socket required for connection to the PMR-5. They also require new firmware. If they have been fitted with the humidity sensor option then this will be disabled when the porometer is in use. The PMR-5 is a hand held cuvette with integral air supply, using an open system measurement of leaf transpiration. The air supply is mass-flow controlled, with manual control of humidity up to ambient. The cuvette clips onto a leaf exposing a 25mm x 5mm section of leaf. It is designed to couple the leaf to the ambient temperature using a fan, a heat sink, and radiation shield. There is a stirring fan in the cuvette to minimise the boundary layer resistance. The CMOS digital combined humidity and temperature sensors monitor the air entering and leaving the cuvette. These are sited close together in an aluminium block with tortuous air paths to minimise temperature gradients between the two sensors.

Technical Specifications

EGM-4 Environmental Gas Monitor Refer to the Technical Specifications in the EGM-4 Operator’s Manual.

PMR-5 Steady State Porometer

Cuvette Housing

Aluminium alloy Cuvette head Aluminium alloy with Perspex/Plexiglass radiation shield covering the head to

minimise heating. A fan-ventilated heat sink is fitted. Window

Coated glass Interference filter that transmits largely below 0.7 microns (< 50% transmission at 0.71 microns) to further decrease Infra red radiation on the leaf.

Humidity/Temperature Sensors

2 CMOS digital sensors. Calibration Accuracy

RH Absolute = 2%. Differential better than 1% by regular programmable sensor matching.

Temperature 0.50 C PAR Sensor

Fully cosine corrected PAR sensor (See PAR-1 specification). Conductance Measuring Range

0-9999 mmol m-2 s-1


Technical Specifications

Conductance Measurement Accuracy

<40 mmol m-2 s-1 = 10%. >40 mmol m-2 s-1 = 20%.

Dimensions

Overall: 285 mm Length x 32 mm Diameter. Window: 25 mm Width x 5 mm Length.

Weight

0.44 kg

Integral Air Supply Unit Air Supply Pump Miniature 6V rotary air pump delivering 0-200 ml min-1 Flow Control and Measurement By mass flow meter, accurate to ± 2% FSD. Input RH Control From dry to ambient RH by proportional diversion of the input air through a drying column.

PP Systems is continuously updating its products and reserves the right to amend its specifications without notice.


Porometer Layout

Porometer Layout

PIVOT PIN HUMIDITY

CONTROL KNOB

LEFT HAND

DRIER BUNG.

DRIER VIEW PORTS

PAR SPAN

PAR ZERO

FIGURE 1 VIEW OF PMR FROM LEFT HAND SIDE The H2O absorber column (orange colour) can be seen through the row of holes on the side of the instrument. The absorber is serviced through plug on the top of the unit.


Porometer Layout

DRIER BUNG

RIGHT HAND PIVOT PIN

PAR SENSOR

STIRRING MOTOR

FLOW CONTROL

KNOB

FIGURE 2 VIEW OF PMR FROM RIGHT HAND SIDE


Porometer Layout

DRIER BUNG

PAR SENSOR

PIVOT PINS HUMIDITY

CONTROL KNOB

FLOW CONTROL

KNOB.

FIGURE 3 VIEW OF PMR FROM TOP


Use as a Porometer

FIGURE 4 ELECTRICAL CONNECTIONS TO THE EGM

Use as a Porometer

Operation Before switching on the EGM, make the two electrical connections to the porometer. These are shown in Figure 4. The 15 pin D should be plugged into one of the I/O sockets on the EGM. Carefully tighten the two retaining screws. The digital connection should be made to the 4-pin socket adjacent to the I/O sockets. The 4-pin connector is pushed in and then the collar should be rotated GENTLY clockwise. THIS MUST NOT BE OVER-TIGHTENED. If the porometer is used in high ambient temperatures, to prevent excessive temperature rise the unit should be kept shaded as much as possible and should not be placed on the ground where temperatures may be very high. For the EGM to recognise that it is connected to a porometer when it is powered up, it must be set to probe inputs and not millivolts (see SET Menu below). It is recommended that the memory be cleared before commencing measurements (see the EGM-4 Operator’s Manual). Otherwise, the porometer measurements will be appended to the end of any measurements already held in the database, and may be difficult to identify.


Use as a Porometer

Adjustment and Selection of Flow and Humidity Air is supplied to the cuvette by an air pump at a flow rate controlled and measured by a mass-flow transducer. The flow knob (blue ended) on the right-hand front of the cuvette handle sets the inlet airflow rate. Clockwise rotation increases the flow. Initially, the flow rate should be adjusted to approximately 100 ml min-1. The humidity of the inlet air can be decreased from ambient by passing varying proportions through a drying column. The humidity control knob (Aluminium ended), is on the left hand rear of the cuvette handle. Rotating the knob clockwise decreases the humidity. Always be gentle and do not force the knob particularly at the end of its travel. Initially set fully anti-clockwise so that the air is at ambient. Close the cuvette and wait a minute a few minutes for stability. If necessary, you should now balance the sensors. The humidity measured is now the ambient. The objective is to adjust the inlet humidity so that the humidity seen by the leaf matches the ambient humidity. Because of the very rapid stirring of the air in the cuvette, the flow rate within the cuvette greatly exceeds the flow through the cuvette. This means that the air flowing out of the cuvette is representative of the air that is circulating over the leaf in the cuvette and due to transpiration, the outgoing humidity must be greater than the inlet. Therefore you should decrease the inlet humidity to give the outlet humidity close to the ambient. However, there is an interaction between the flow rate and the humidity entering the leaf cuvette so it is recommended that the flow-rate be set first and then the humidity adjusted. A typical sample leaf should now be placed in the cuvette and the flow rate adjusted to give at least 2 mb difference between inlet and outlet. Decreasing the flow rate increases the difference, but the flow rate should be kept above 50 ml.min-1. The humidity entering the cuvette should now be decreased so that the cuvette humidity is close to the ambient. Note, the cuvette relative humidity should be kept below 70 % for accurate results. (See Table below).

Cuvette Air temperature oC

Maximum Cuvette Vapour Pressure For 70% RH

0 4.3 5 6.1

10 8.6 15 11.9 20 16.4 25 22.2 30 29.7 35 39.4 40 51.6 45 67.1 50 86.4

Within a few seconds of enclosing a leaf in the cuvette, the readings will stabilise and will then slowly alter as the final equilibrium is established. It is suggested that recordings should be made as soon as the conductance reading is changing only slowly (typically after 15-30 seconds). If left too long, the stomata will start to adapt to the new conditions. It is important to note that stressed leaves appear to respond faster than unstressed leaves.


Use as a Porometer

Power On When the instrument is first powered up, it will go through its normal warm-up period that takes approximately 5 minutes. Immediately after powering up the system, the following is displayed:

PP SYSTEMS C2002 EGML nnnn V1.50

Where : EGML is for analysers with a maximum measurement range of 0 to 30000ppm EGMH is for analysers with a maximum measurement range of 0 to 99999ppm nnnn is the instrument Serial Number V1.50 is the firmware version number These must be quoted in any communications with PP Systems about the unit . NB Only EGM firmware versions of 1.4 and greater can be used with the PMR-5 and, as the linearisation for the porometer flowmeter is in the EGM firmware, this is specific to a single porometer.

Main Menu Then the Main Menu is displayed:

1REC 2SET 3CAL 4DMP 5CLR 6CLK

Where:

Press Key To 1 Go Into Measurement Mode 2 Change system settings

(zero type and time interval, recording type, alarm settings, etc.) 3 To calibrate the analyser 4 To dump stored data to a PC or to view data on the LCD display 5 Clear system memory 6 Set/check the system clock (date and time)

For details of the above options, refer to EGM-4 Operator’s Manual.


Use as a Porometer

SET Menu Before using the PMR-5, the EGM needs to be set to read PROBE INPUTS. The following menu is displayed:

1EGM 2Z 3PMP 4AV 5RECD 6ALM 7VOUT

Then press Key 1 (EGM) to display:

EGM 1:MV 2:PROBE Y=OK 1 / 2=CHANGE

The current selection is indicated by ( * ) replacing the number. Press Key 2 to select for the Porometer and then press Key Y twice to return to the Main Menu.

REC Menu To make measurements select REC from the Main Menu. The operator is now taken through the series of actions required before a measurement can be made. Press the N Key at any point to quit and return to the Main Menu. The following message is displayed:

Cnnnnn nV=nnnnn Porometer. Rnnn

Where: Cnnnnn is the last calibration gas concentration. After DEFAULT it is the original range specified by the customer. nV=nnnnn is the range of the output voltage signal corresponding to the CO2 concentration e.g. 1V=2000. This can be altered through SET. After DEFAULT it will be 5V=Range specified by the customer. Rnnnn is the current total of the records stored in the memory. NB if “mV Inputs” is displayed instead of “Porometer” then it will be necessary to set the EGM to Probe Inputs through the SET Menu. This may be followed by a delay of approximately 45 seconds to allow for calibration of the electronics and then the instrument proceeds to warm-up until the analyser temperature reaches 50 C. The EGM now checks that there are humidity reads from the porometer sensors. If all is well then the Porometer Displays are shown.


Use as a Porometer

If there is a problem with the sensor reads then the following error message is displayed:

PMR PRESENT BUT NO HUMIDITY READ

The display then returns to the Main Menu. If this message is shown then check the 4 pin round connector from the porometer to the EGM for correct insertion and then try again. NOTE WARNING ABOUT GENTLE INSERTION AND TIGHTENING. If the problem persists then the EGM should be opened and the internal connection from the 4-pin connector to CN8 on the motherboard should be checked.

6-PIN HEADER ON EGM BOARD.

PIN 1 MARKED WITH WHITE

4-PIN PMR

SOCKET.


Use as a Porometer

The first three displays are for setting up porometer. They are only shown the first time through after switching on the EGM. The EGM must be switched off and then on again to display them again.

Porometer Display 1 (Serial Number input)

ENTER PMR NO XXX The Porometer serial number is 3 digits (001 to 999) and this entry is done to confirm that the flowmeter calibration in the EGM firmware corresponds to the serial number of the connected porometer. If the correct value is not entered then the display returns to the Main Menu. Another attempt can then be made in the event of an input error. The next display is used to set Rb and leaf area.

Porometer Display 2 (Rb/Area setting)

1: RB = 0.30 2: AREA = 1.25

These are the default values for the standard porometer but for greatest accuracy the RB value for your porometer shown on the TESTED label should be entered. To accept press Key Y or to change press Key 1 or 2.

Porometer Display 3 (selection of Light Type to set TRANS)

*:SUN/SKY 2:LED 3 TUNGSTEN

For the energy balance calculation of leaf temperature it is necessary to know the energy of the radiation absorbed by the leaf. The PAR is measured external to the radiation shield and window and the PAR is converted to the absorbed value using a conversion factor, (TRANS Coefficient). This value depends on the source of the incident radiation.

Source TRANS Coefficient

SUN/SKY 0.13 LED (includes fluorescent lighting, and other Discharge lamps) 0.11

TUNGSTEN (All incandescent Lamps) 0.14 The current selection is indicated by ( * ) replacing the number. Enter the number required and press Key Y to continue.


Use as a Porometer

Porometer Display 4 (Sensor Balance)

KEY 2 = HUMIDITY SENSOR BALANCE

This is a reminder that the sensors should be aligned on first entering the measurement mode (see SENSOR BALANCE below). After approximately 3 seconds the following is displayed to allow entry of record and plot number,if required.

Porometer Display 5 (Record and Plot Number)

REC 0001 PLOT 00 03-04 12:40

Where:

REC Records collected using the current PLOT number (up to 9999). PLOT PLOT Number, a user changeable number from 00 to 99 03-04 Date (3rd day of April) 12:40 Time (12:40 PM)

If the plot number needs to be changed, press Key N and enter the plot number desired. Press Key Y to continue. NB. Only the plot number can be changed at this point. The record number automatically resets to 1 when the plot number is changed. At any time during the porometer measurements, the plot number can be changed by using Key 8/X (Exchange) to return to this display and then following the above instructions. Press Key 8/X to proceed to the Porometer Measurement Display.


Use as a Porometer

Porometer Display 6 (Measurement Display/Record)

I22.3 O23.4 T22 Q1645 F145 G0141

Where:

I Inlet watervapour pressure (mb) O Outlet water vapour pressure (mb) T Porometer Temperature (°C) Q PAR (µmol m-2 s-1) F Flow Rate (ml min-1) G Stomatal Conductance (mmol m-² s-¹ )

The stomatal conductance calculation uses an exact determination of the leaf temperature by the energy balance method. To balance the humidity sensors press Key 2 (see SENSOR BALANCE below). To record press Key Y/R Key 8/X can be used to rotate round the CO2 Concentration Display 7, the Plot Number Display 5, and the Measurement Display 6. To return to the Main Menu while in Measurement Mode, simply press Key N.

Sensor Balance The EGM assumes that the sensor response is linear and that the sensor zeroes are correct. The balance (alignment) consists of calculating a multiplier that, when applied to the sensor readings, makes them both read the average of their two values. This can only done when you are in the MEASUREMENT DISPLAY. This should be done at the start of measurements and may be repeated at any time during the measurements. TO ALIGN THE SENSOR READINGS THE CUVETTE MUST BE CLOSED WITHOUT ANY LEAF and the humidity should be set to the anticipated measurement value. TO ALIGN THE SENSOR READINGS THE CUVETTE MUST BE CLOSED WITHOUT ANY LEAF When the humidity readings are STEADY Key 2 should be pressed. On completion the following is briefly displayed.

HUMIDITY BALANCE COMPLETED

The display then returns to the measurement display.


Use as a Porometer

Adjustment and Selection of Flow and Humidity Cuvette Flow Rate Air is supplied to the cuvette by an air pump at a flow rate controlled and measured by a mass-flow transducer. The inlet airflow control knob (blue ended) is on the right-hand front of the cuvette handle. Rotating the knob clockwise increases the flow. Initially, the flow rate should be adjusted to about 75 ml min-1 , (an approximate flow rate of 1 cm3 s-1 cm-2 of exposed leaf). A typical sample leaf should now be placed in the cuvette and the flow rate adjusted to give at least 2 mb difference between inlet and outlet. Decreasing the flow rate increases the difference, but the flow rate should be kept above 30 ml.min-1 if possible. Cuvette Humidity The humidity of the inlet air can be decreased from ambient by passing varying proportions through a drying column. The humidity control knob (grey ended) is on the left hand rear of the cuvette handle. Rotating the knob clockwise decreases the humidity. Because of the very rapid stirring of the air in the cuvette, the flow rate within the cuvette greatly exceeds the flow through the cuvette. This means that the air flowing out of the cuvette is representative of the air that is circulating over the leaf in the cuvette. Therefore the objective should be to adjust the inlet humidity to give the outlet humidity close to the ambient. It is recommended that the outlet humidity should not exceed 70% RH for accurate measurements. Within a few seconds of enclosing a leaf in the cuvette, the readings will stabilise and will then slowly alter as the final equilibrium is established. It is suggested that recordings should be made as soon as the conductance reading is changing only slowly (typically after 15-30 seconds). If left too long, the stomata will start to adapt to the new conditions. NB. Stressed leaves appear to respond faster than unstressed. When the humidity readings have stabilised press Key Y/R to take a record.

Cuvette Humidity Error If the Relative humidity of the air in the cuvette exceeds 75%, based on the ratio of the cuvette vapour pressure to the saturated vapour pressure at the leaf temperature, then the following is displayed:

CHAMBER RH >75% CHECK FLOW/RHIN

Above this humidity errors in measurements can rapidly increase so the humidity should be decreased by either increasing flow and/or decreasing inlet humidity.


Use as a Porometer

Porometer Display 7 ( CO2 Concentration and Atmospheric Pressure) While in Measurement Display, pressing Key 8/X shows CO2 concentration, atmospheric pressure and probe type:

C 365 A 0998 P 07

Where:

C CO2 concentration (ppm) H Humidity (mb). Only if a sensor is present. AT Atmospheric Pressure (mb) PT Probe Type

Press Key 8/X, once for Plot Number and once for Measurement Display.


Calculations

Calculations The following details the calculations used in the porometer program. Let :- Ti = Temperature of the inlet air RH sensor (°C) Ta = Air temperature in porometer measured =

temperature of the outlet air RH sensor. (°C)

Tl = Leaf temperature. (°C) ei = Water vapour pressure in the inlet air (mbar) ea = Water vapour pressure in the outlet air (mbar) esi = Saturated water vapour pressure at Ti (mbar) esa = Saturated water vapour pressure at Ta (mbar) esl = Saturated water vapour pressure at TI (mbar) Ri = Inlet air relative humidity (%) Ro = Outlet air relative humidity (%) A = Leaf area exposed in the porometer (cm2) E = Transpiration rate (mol m-2 s-1) H = Heat energy absorbed by the leaf. W m-2 V = Flow rate of air into the porometer (ml min-1 at 0° C & 1013mb) W = Mass Flow rate of air per unit leaf area (mol m-2 s-1) ó = Stefan Boltzmann's constant. P = Atmospheric pressure (mb) rb = Boundary layer resistance to water vapour (m-2 s-1 mol-1) rs = Stomatal resistance (m-2 s-1 mol-1) Gs = Stomatal conductance = 1/rs (mol m-2 s-1) ρ = Air density ( kg m-3) Cp = Specific heat of air at constant temperature (J kg-1 K-1) α = (TRANS) =Conversion factor from incident quanta

to energy absorbed by the leaf (W m-2) / (µmol m-2 s-1)

λ = Latent heat of vaporisation of water (J kg-1) Q = Quantum flux rate measured between 0.4 and 0.7

microns (µmol m-2 s-1) (PAR incident on the cuvette.)

Step 1 Inlet and outlet %RH readings are converted to the water vapour pressure in mb. This gives more accurate measurements than using the %RH readings as the temperature measurements of each sensor are taken into account. This is transparent to the user and at no stage are %RH readings shown though an error warning is given if the cuvette humidity exceeds 75%

ei = Ri* esi

and ea = Ra * esa


Calculations

Step 2 Calculate the mass flow of air per unit leaf area entering the cuvette (W). The CIRAS mass flowmeter is calibrated to read the volume flow at 20o C & 1 bar (V). Since the molar volume is 22.414 at 0o C and 1 standard atmosphere, then:- W = (V / 1,000) x (1 / 22.414) x (273 / 293) x (1 / 1.013) x (10,000 / A) STEP 3 The Transpiration rate (E) is now calculated from the water vapour pressure of the air entering (ei) and leaving the cuvette (ea). The molar flow of water into the cuvette is:- (ei / P) x W mol m-2 s-1 The molar flow of air out of the cuvette, due to the addition of the transpired water, is (E+W). Therefore, the molar flow of water out of the cuvette is:- (ea / P) x (E + W) mol m-2 s-1 But the difference between the molar flows into and out of the cuvette must equal the transpiration, thus:- E = [(W + E) x (ea / P)] - (W x ei / P) Therefore:- E = [W x (ea - ei)] / (P - ea) STEP 4 The leaf temperature (Tl) is now calculated from the energy balance. It can be shown (Reference 1) that the difference between air and leaf temperature is as follows:-

∆T = (H - λ E) / (0.93 x ρ x Cp /rb + [4ó x (Ta + 273)3)] Tl = Ta + ∆T 0.93 converts rb to the resistance to convective transfer of heat. H is calculated from the Photon flux incident on the cuvette (Q), taking into account the ratio of infrared to PAR in the light source, the transmission through the windows, and reflection/absorption by the leaf.( H = Q * α) In the program, the following approximation is made:- 4ó x (tc + 273)3 - > > 4.639 + (0.0583 x tc)


Calculations

STEP 5 From the leaf temperature, we can derive the saturated vapour pressure at leaf temperature (esl) and the stomatal resistance (rs). From step 2:- E = W x (ea - ei) / (P - ea) but also:- E = (esl - ea) / [P x (rs + rb)] therefore:- rs = [[(esl - ea) / (ea - ei) x (P - ea) / P] / W] - rb but:- (P - ea) / [(ea - ei) x W] = 1 / E therefore:- rs = [(esl - ea) / (E x P)] - rb and:- gs = 1 / rs


RS232 Data Transfer

RS232 Data Transfer Stored data can be viewed on the instrument LCD display, or transmitted to the PC computer using the Windows data transfer software (see the EGM-4 Operator’s Manual). N.B.If there are no stored records, then the message “NO MORE RECORDS IN STORE” will be displayed before returning to the Main Menu.

Record Structure A single record consists of one line, 61 digits in length. Real-time and stored data is output in the following format::

M/R Plot No.

Rec No Day Month Hour Minute CO2 ppm

E Ta

M XX XXXX XX XX XX XX XXXXX XX.X XXX.X

PAR ei Tl ea V GS ATMP PROBE XXXX XXX.X XXX.X XXX.X XXX.X 0000 00 00 nnnn 7

Where: M/R M = Real Time Measurement

R = Record from memory Plot No. 0-99 Rec No. 1-9999 Day 1-31 Month 1-12 (January - December) Hour 1-24 (based on 24 hour clock) Minute 0-59 CO2 Ref 0-99999 CO2 reading in parts per million (ppm =µmol m2 s-1) E 0- 99.9 Evaporation rate in millimol m2 s-1 Ta - 40 to + 99.9 Cuvette Temperature PAR Incident Par 0-3000 µmol m2 s-1 ei Reference millibars 0-= 99.9 Tl Leaf temperature 0-99.9 ea Analysis millibars 0-= 99.9 V Air flow ml/minute 0-200 Gs Stomatal Conductance 0-9999 mol.m-2.s-1 2 Digits not used 2 Digits not used ATMP 0-1099. Atmospheric pressure in millibars (mb) Probetype 2 digits.Porometer = 07


Daily Checks

Daily Checks Cuvette Head and Leaf Seals After each day's use, the cuvette should be examined for the following. 1) Foreign matter Debris inside the cuvette will affect the response time and should be

carefully removed with a brush or lint-free cloth. To fully access the head, detach the head opening assembly by undoing the large thumb screws either side of the top head plate.

2) Damage to the leaf seal. A quick visual inspection should be done, and if there is obvious

damage the seal should be replaced. Occasionally the cuvette should be checked for leaks. This is done by operating in the normal way, but without a leaf in the system. Check for any change in measured humidity while breathing hard over the cuvette head. If there is an increase then the leak can often be isolated by gently blowing onto localised positions through a pipe. Replace the gasket by detaching the head opening assembly. New gasket should be carefully cut from the supplied gasket material to correspond with the cuvette opening.

Envirogel Air Drier The recommended drier is self-indicating Envirogel. The indicator changes from orange to green when exhausted. Refer to the Manufacturers’ Safety Data Sheet (available through our web site for registered users) for instructions in use. The drier is visible through the series of holes on the rear LHS of the handle. This is best done in bright light. When all the holes show green then the drier should be replaced. Place the cuvette on a soft surface. Pull out the bung on the top of the rear of the handle. Tip the contents of the absorber column into a suitable receptacle. Now carefully refill the column using a funnel or a paper cone, tapping gently to settle the contents. Fill until level with the bottom of the bung hole. Refit the bung. Please refer to the EGM-4 Operator’s Manual for more details regarding analyser maintenance.

Storage When not in use the porometer should be stored in the open position with the spring pressure off the leaf seal. A small length of 3mm OD pipe is ideal for this purpose. Storage should not be at excessive humidity (>70%) or temperature (>35° C).


Calibration

Calibration The humidity, temperature and flow sensors cannot be re-calibrated. The only sensor that can be calibrated is the PAR. PAR Calibration It is not necessary to dismantle the porometer cuvette for PAR sensor calibration, as the two adjustment potentiometers (ZERO and SPAN) are accessible through holes in the handle. These are situated on the LHS of the handle. The light sensor is a filtered silicon cell and should be re-calibrated when necessary against a suitable quantum sensor. There is no significant interaction between the zero and span controls. Note. If the photocell is replaced, re-calibration- is essential. 1) To set the zero, simply cover the PAR sensor. If necessary, adjust the ZERO

potentiometer to obtain a zero reading. The pot nearest the cuvette head is ZERO.

2) To set the span, it is recommended that the sensor be exposed to a stable light source and checked against a suitable quantum sensor. If necessary, adjust the SPAN potentiometer until the sensor reading is correct. The pot furthest away from the cuvette head is SPAN.

Maintenance Replacement of the cuvette stirring motor 1) Place the cuvette on a soft surface. 2) Detach the head opening assembly by unscrewing the pivot pins 3) Undo the 2 screws, one each side of the heat sink. 4) Remove the 8 head plate screws. 5) Remove the fan-bale by gently pulling up. 6) Undo the 2 screws that retain the motor. 7) Make CAREFUL NOTE of how the motor is wired. Cut the wires to motor. Solder and

sleeve the wires to the replacement motor observing the correct polarity. N.B. The fan must rotate in an anti-clockwise direction.

8) Lightly grease the motor face before re-fitting. After screwing in place, refit fan and check for free rotation.

9) Lightly grease the head-plate with silicone and replace, gently and uniformly tightening the 8 screws.

10) Complete re-assembly. Replacement of the cooling fan 1) Remove the 2 retaining screws, noting WITH GREAT CARE the position of all washers

and spacers, as they must be re-assembled exactly as found. 2) Cut existing fan motor wire and solder and sleeve to the new fan motor, observing the

polarity. 3) Re-assemble with washers and spacers exactly as originally supplied. Replacement of the air supply pump To replace the pump it is necessary to dismantle the instrument. This is a long life unit running under light load and failure is unlikely. If the pump fails in service then instructions for fitting will be supplied with the replacement pump.


Diagnostics


Diagnostics The Humidity sensor diagnostics display described in the EGM-4 Manual is modified when the PMR-5 is connected:

I/O aaa bb.b cc.c ddd ee.e ff.f

I/O refers to the inlet and outlet RH/Temperature sensors and the readings alternate at 3 second intervals. The top line refers to the Humidity readings. aaa is the raw read from the sensor. bb.b is after conversion to %RH. cc.c is conversion to mb using the saturated water vapour pressure at the sensor temperature. The bottom line refers to the sensor temperature readings. ddd is the raw read from the sensor. ee.e is the conversion of this to degrees Celsius. ff.f is the calculated saturated vapour pressure at this temperature. This is used in the calculation of the vapour pressure. (cc.c = bb.b * ff.f). Key N will quit Diagnostics. Key Y will go to the next display. The EGM will take up to 6 seconds to respond to the Key. All the other displays are as described in the EGM-4.Manual. N.B. INPUTB = PAR, INPUTD = Cuvette air Flowmeter

PMR-5 STEADY STATE POROMETER OPERATOR'S MANUAL Version · PDF filePMR-5 STEADY STATE POROMETER OPERATOR'S MANUAL Version 5.02 © 2006 PP Systems. All Rights Reserved 17 October...

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