HRM FAQs

How long is the "useful life" of the HRM once set up in the tree?
What is the warranty period for the HRM sensor?
How do I maintain the HRM when not installed in a tree?
Maintaining HRM in the tree - Should I do something while the sensor is installed in the tree?
How many HRM sensors per stem or tree do you suggest to get representative data? Is one sensor enough to start on the field?
Do you have any papers published about the HRM sensor? I mean some references for the vineyards associations, research centres in Australia or in another country?
Can the HRM measure mangrove trees?
Is the HRM water proof?
Is the HRM rust proof?
How frequently does the HRM require calibration?
Does rainfall, affect HRM Measurement?

How long is the "useful life" of the HRM once set up in the tree?

The HRM sensor will last for many years if maintained well; we think 5 years or longer provided they are treated well, maintained and the heater does not blow. The heater is like a light bulb it can last for a very long time or suddenly just blow. At this early stage we have not had any blow!

What is the warranty period for the HRM sensor?

The HRM sensor can continuously log sapflow data for 1 to 2 years without any problems. However, this is species specific as some species may grow faster than others and begin to grow around the sensor and incorporate it into the tree! Also some species may wound more than other species meaning your results become incorrect over time due to the impact of tree wounding which cannot be accounted for.

How do I maintain the HRM when not installed in a tree?

To maintain an HRM sensor they should simply be wiped down with a damp cloth to remove any sap before being put in storage. Also be sure not to bend any of the needles as this could break the very fine thermocouple wires inside the probes. Finally be sure not to leave the probes connected to a logger and pulsing if they are sitting in air. This can cause the heater to burn out.

Maintaining HRM in the tree - Should I do something while the sensor is installed in the tree?

In terms of spares there is really nothing the customer can replace. Possibly the heater probe but this would require a technician to cut off and solder a new one on to the interface and test. So not something we would like the customer to try.

How many HRM sensors per stem or tree do you suggest to get representative data? Is one sensor enough to start on the field?

One HRM sensor would be OK per tree. However, consider an example of two tree discs: one has even growth rings all the way around the tree and the second has very irregular growth rings, some being very close together on one side of the tree but very wide apart on the other side. This was caused by non uniform planting densities and competition from other surrounding dominant and co-dominant trees. In this instance and for detailed scientific research I would recommend 4 sensors per tree and to average the results of these sensors to give an accurate representative total water use figure and also to identify the within tree variation of water use caused by competition.

Do you have any papers published about the HRM sensor? I mean some references for the vineyards associations, research centres in Australia or in another country?

Yes, the web page www.ictinternational.com.au/refhrm.htm lists many HRM publications although they were published using Campbell loggers before the HRM sensor was improved by making it a Smart Sensor. However, I am unaware of publications using the HRM in grapes so this is a great opportunity for the scientist to buy them and make a famous name for themselves because more and more people will be buying the HRM sensors for grapevine study. CSIRO in Australia bought a TDP smart system for measuring Grapevine water use 2 years ago before the HRM was available, this year they will buy another system and it will be HRM not TDP.

Can the HRM measure mangrove trees?

Yes, the sensor is suitable for measuring mangroves.

Is the HRM water proof?

The sensor and digital interface are perfectly water proof, they can be submerged in water and they will not have a problem -- but this would cause measurement problems so it should not be used like this. The only part of the sensor that is not water proof is the end of the sensor cable and the DataBus this must be kept dry at all times otherwise you will create a short circuit.

Is the HRM rust proof?

The cable and interface and the base of the needles are all plastics and epoxys so they are rust proof. The needles are a surgical grade stainless steel therefore they will not rust easily. When they are installed in plants, even plants with very corrosive sap or tannins, they do not rust. But, if they were left lying in the air or in water over a very long time (many years) in a marine environment I think they would eventually rust. Again however, this is not they way the sensors are used so the HRM will have good longevity even in a mangrove or similar type of application.

How frequently does the HRM require calibration?

The sensor itself does not require calibration. If the customer is just wanting to measure raw Heat Pulse velocities (e.g. just wants relative measures of sapflow or a graph of how the plant is responding to water use) then again no calibration is required. However, if the customer wants corrected sap velocity measurements (cm/hr) or corrected sapflow measurements (g/hr) then each time the sensor is installed a range of parameters must be recorded such as Thermal Diffusivity, Base Line Asymmetry multiplier and offset, Wounding Coefficient, VsFactor (a multiplier to convert from Heat Pulse velocities Vc to Corrected Sap Velocities Vs which is obtained through measuring the fractions of sap and wood in the xylem and accounting for their differing densities and specific heat capacities) and sapwood area (for Sapflow only). These parameters must be collected for each installation of the sensor and can either be stored in the memory of the sensor's microprocessor or entered into a spreadsheet for post processing of the raw heat pulse velocities after the data has been collected.

Does rainfall, affect HRM Measurement?

No there is no problem because the thermocouples are installed in the stem of the plant therefore any stem flow (water running down the outside of the stem) will not affect the measurement. This is typically only a problem for Energy balance or Dynagage sensors that attach to the outside of the stem and which have not been correctly installed to divert the water away from the measuring thermocouples of the sensor.

HRM FAQs

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