Campbell CR23X Spécifications télécharger pdf (Page 279)

F-1

APPENDIX F. DYNAGAGE SAP-FLOW (P67)

F1. FUNCTION

The Dynagage Processing Instruction, P67, is

used in conjunction with a Dynamax, Inc.

Dynagage stem flow gage. Instruction 67

calculates the sap flow rate within a plant stem

by using an energy balance equation and inputs

from a Dynagage sensor.

Briefly, the energy input into the stem is a

known quantity (Q

h

), conductive radial and

vertical energy losses are calculated (Q

r

and Q

v

,

respectively). The residual energy is assumed

lost through sap flow (Q

f

) and is given as:

Q

f

= Q

h

- (Q

r

+ Q

v

).

By measuring the change in temperature (dT) of

the stem by heating and assuming 4.186 Joules

of energy are required to heat each gram of sap

1° C, the flow rate can be calculated.

Accumulated flow can be calculated using

datalogger Instruction 72 (Totalize).

F2. INSTRUCTION DETAILS

Dynagage Sap-Flow (P67)

1: 0000 Begin Input Location

[ _________ ]

2: 0.0 K

sh

(W/mV)

3: 0.0 Heater Resistance(Ohm)

4: 0.0 Stem Area (sq cm)

5: 0.0 Thermal Conductivity

(W/m∗K)

6: 0.0 Thermocouple Gap (cm)

7: 0.0 Low-Flow Cutoff

Temperature (C)

8: 0.0 High-Flow Cutoff Velocity

(cm/s)

9: 00 Output

10: 0000 Destination Input Location

[ _________ ]

11: 0.0 Mult

12: 0.0 Offset

F2.1 INPUT VOLTAGES

PARAMETER 1

Four voltages must be stored sequentially

beginning with the Input Loc option stated in

Parameter 1.

INPUT LOCATION

Loc 1: Ch (Thermopile (mV))

Loc 2: Ah (Upper TC (mV))

Loc 3: Bh (Lower TC (mV))

Loc 4: Voltage Input

These voltages are measured using Instruction

2. Voltages for locations 1-3 are measured on

the 2.5 mV slow range. The voltage for location

4 is measured on the 2500 mV slow range.

F2.2 CONSTANTS

Parameters 2 through 6 are constants that must

be entered for each Dynagage.

PARAMETER 2

K

sh

(W/mV), a constant required to relate the

thermopile output proportionally to the radial

heat transfer.

PARAMETER 3

The heater resistance (Ohms), measured with

an Ohm meter.

PARAMETER 4

The cross sectional area of the stem (sq cm).

PARAMETER 5

Thermal conductivity (W/m∗K). This number is

generally 0.54 W/m∗K for herbaceous plants or

0.42 W/m∗K for woody plants.

PARAMETER 6

Thermocouple gap (cm) is the distance

between the thermocouples in the Dynagage,

measured in cm. This value is determined by

Dynamax and is found in the Dynagage

documentation.

F2.3 FILTERS

Two predictable conditions may occur when the

output from the Dynagage is not valid. In these

cases, the output must be "filtered" so only

reasonable flow rates are processed. These

conditions are very low flow rates and high flow

rates, both of which cause dT to approach zero.

The values generally placed in Parameters 7

1 2 ... 274 275 276 277 278 279 280 281 282 283 284 ... 373 374

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