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229 Heat Dissipation Matric Water Potential Sensor

9. References

Flint, A. L., G. S. Campbell, K. M. Ellett, and C. Calissendorff. 2002. Calibration
and Temperature Correction of Heat Dissipation Matric Potential Sensors. Soil
Sci. Soc. Am. J. 66:1439–1445.

Reece, C.F. 1996. Evaluation of a line heat dissipation sensor for measuring soil
matric potential. Soil Sci. Soc. Am. J. 60:1022–1028.

Summary of Contents for 229

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Page 3: ...e repair is under guarantee or not Please state the faults as clearly as possible and if the product is out of the guarantee period it should be accompanied by a purchase order Quotations for repairs...

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Page 5: ...l cell phones and aerials may also not be applicable according to your locality Some brackets shields and enclosure options including wiring are not sold as standard items in the European market in so...

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Page 7: ...ram Structure and Multiplexers 6 5 4 Temperature Correction 7 5 5 Example 1 CR1000 with CE4 and Four 229s 8 5 6 Example 2 CR1000 with AM16 32 series Multiplexer CE4 and Sixteen 229 Sensors with Temper...

Page 8: ...libration 19 6 2 Measurement error for range of soil temperatures and wide range of matric potential 21 6 3 Measurement error for range of soil temperatures and wetter range of matric potential 22 6 4...

Page 9: ...ongitudinal section of the needle with heater and thermocouple junction The ceramic cylinder has a diameter of 1 5 cm and a length of 3 2 cm Three copper wires and one constantan wire contained in a s...

Page 10: ...r potential gradient exists When the water potential of the soil surrounding a 229 sensor changes a water flux with the ceramic matrix will occur The time required for hydraulic equilibration of the w...

Page 11: ...esents a typical temperature response in a silt loam 0 5 1 1 5 2 2 5 3 0 5 10 15 20 25 30 heating time s temperature increase C 200 kPa 100 kPa 50 kPa 10 kPa Figure 1 3 Typical Temperature Response of...

Page 12: ...urrounding the ceramic portion with a slurry of fine silica sometimes referred to as silica flour 3 3 Equilibration and Saturation of the Sensor Before Installation The smaller the difference in water...

Page 13: ...ol Port CTRL Figure 4 1 Schematic of Connections for Measurement of a 229 Sensor 5 Example Programs 5 1 Choosing a Reference for the Thermocouple Readings A fundamental thermocouple circuit uses two t...

Page 14: ...properties of the needle casing wiring and the amount of contact area between the needle and the ceramic have a slight effect on the temperature response Most of the non ideal behaviour of the sensor...

Page 15: ...echanical relays This degradation will adversely affect the suitability of these relays to multiplex low voltage signals Although a relay used in this manner no longer qualifies for low voltage measur...

Page 16: ...iring information for reading four 229 sensors with a CR1000 datalogger and CE4 current excitation module Table 5 1 Wiring for Four 229s with CR1000 and CE4 229 CR1000 229 CE4 229 1Blue 1H 229 1 Green...

Page 17: ...iff StartTemp_C Num229 mV2_5C 1 TypeT RefTemp_C True 0 _60Hz 1 0 PortSet 1 1 Set C1 high to activate CE4 Delay 0 1 Sec Wait 1 second Measure temperature after 1 second of heating TCDiff Temp_1sec_C Nu...

Page 18: ...E4 Wiring with CR1000 and AM16 32 series 229 107 Function CR1000 CE4 Multiplexer 4x16 mode Blue 229 Thermocouple High ODD H 1H 3H etc Red 229 Thermocouple Low ODD L 1L 3L etc Green 229 Heater High EVE...

Page 19: ...e are examples dTdry 1 3 421 dTdry 2 3 417 dTdry 3 3 433 dTdry 4 3 418 dTdry 5 3 412 dTdry 6 3 407 dTdry 7 3 422 dTdry 8 3 428 dTdry 9 3 399 dTdry 10 3 377 dTdry 11 3 405 dTdry 12 3 406 dTdry 13 3 422...

Page 20: ...Tables and Store Data Flag 1 False Disable 229 measurements NextScan EndProg 5 7 Example 3 CR10X with 229 Sensor Table 5 3 shows wiring information for reading a single sensor with a CR10X datalogger...

Page 21: ...ermocouple Temp DIFF P14 Measure initial sensor temperature 1 1 Reps 2 1 2 5 mV Slow Range 3 1 DIFF Channel 4 1 Type T Copper Constantan 5 1 Ref Temp Deg C Loc Ref_Temp 6 2 Loc Tinit_1 7 1 0 Mult 8 0...

Page 22: ...Constantan 5 1 Ref Temp Deg C Loc ref_temp 6 4 Loc T30sec_1 7 1 0 Mult 8 0 0 Offset 10 Do P86 turn off CE8 1 52 Set Port 2 Low 11 Z X Y P35 Calculate delta T 1 4 X Loc T30sec_1 2 3 Y Loc T1sec_1 3 5 Z...

Page 23: ...H etc Red 229 Thermocouple Low ODD L 1L 3L etc Green 229 Heater High EVEN H 2H 4H etc Black 229 Heater Low EVEN L 2L 4L etc Clear 229 Shield G CE4 CE8 Power 12V 12V CE4 CE8 Ground G CE4 CE8 Enable C1...

Page 24: ...2 16 Loop Count 6 Do P86 Advance to next multiplexer channel 1 73 Pulse Port 3 7 Temp 107 P11 Measure reference temperature 1 1 Reps This is the same instruction 2 5 SE Channel for both the CR10X and...

Page 25: ...Reject Slow Range 3 1 DIFF Channel 4 1 Type T Copper Constantan 5 2 Ref Temp Deg C Loc Tref_C 6 35 Loc T30s_1 7 1 0 Mult 8 0 0 Offset 14 Do P86 turn off CE8 1 51 Set Port 1 Low 15 Z X Y P35 Calculate...

Page 26: ...ake several forms The most commonly used function is exp T 1 with the soil water potential exp the exponential function T the temperature increase during the chosen heating period of time the slope an...

Page 27: ...0 to 1 with norm T equal 0 for dry soil and 1 for saturated soil The wet T value requires full saturation of the ceramic The ceramic portion of the sensor must be immersed in water while under vacuum...

Page 28: ...is close to the temperature at the time of sensor calibration there is no need for correction The 229 measurement method uses heat transfer away from a heated line source and the heat transfer depends...

Page 29: ...00 600 400 200 0 200 400 600 10 degrees C 16 degrees C 18 degrees C 22 degrees C 24 degrees C 30 degrees C matric potential kPa error kPa Figure 6 2 Measurement error for range of soil temperatures an...

Page 30: ...erature must be used for the calibration variable Normalized temperature is as defined in equation 3 The correction procedure is an iterative method Examples of implementing the iterative routine with...

Page 31: ...o confirm equilibration is to repeat the measurements at a given applied pressure until readings do not change 6 4 General Description of Calibration Measurement Process using Pressure Plate Extractor...

Page 32: ...ermal properties are affected by pressure and calibration data should be collected at the same pressure the sensors will be used in most cases this is atmospheric pressure 6 4 1 Wiring for Calibration...

Page 33: ...to datalogger control ports Check for a good electrical connection on the wires going from the common channels to the datalogger and the current excitation module Check program to make sure that the...

Page 34: ...pbell K M Ellett and C Calissendorff 2002 Calibration and Temperature Correction of Heat Dissipation Matric Potential Sensors Soil Sci Soc Am J 66 1439 1445 Reece C F 1996 Evaluation of a line heat di...

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