Met Instruments Project

Moving Forward with Project CAPE

After taking some time to think through the best way to execute data observation for project Collection of Atmospheric Pressure data Experiment (CAPE), I think I have come up with a pretty good solution.

The main components of every mobile mesonet are the:

  • Anemometer
  • Fast Temperature Sensor
  • T/RH Probe
  • Barometric Pressure Sensor
  • GPS Receiver
  • Electronic Compass
  • Data logger

These are the very basic instruments that allow for standard atmospheric conditions to be observed via a moving platform. In our case, we have already acquired the anemometers (05103), data loggers (CR23X), and technically our T/RH proves (HMP35C). I say technically because Campbell Scientific still offers calibration services for these sensors. While at the time of writing this I have sent and inquiry their way and await a response, I can’t imagine they don’t still. Why? Well, if they still offer limited support for data loggers deployed in the 80’s, who’s to say they don’t still provide support for their sensors?

Sure, there is inherent risk involved with going this route, using sensors retired for just over a decade and with non-replaceable parts. One might consider this a dead end and a waste of time and money sure. All valid concerns. However: the cost of each sensor is negligible compared to the modern replacement. $900 versus $50. One doesn’t even have to do the math to consider the latter a better option. While sure, the HMP155A has an accuracy greater than the HMP35C, but by what, a single percentage? I’d consider that negligible if one can get an older sensor calibrated and operation under half of what it would cost to purchase a modern probe. Add $200 or so for calibration from CSI and you are still just over a quarter of what a modern sensor + calibration would cost.

While CSI is unable to replace faulty parts, buying up several of the same sensor to compensate for the potential loss due to drift outside of acceptable range, you still haven’t met the cost of a single new probe, with change to spare.

Furthermore, I can’t help but think the sensors sold and acquired on the second hand market are good for more than a few years yet. I consider this because while the organization may have retired the sensors for a newer upgrade, that has no impact on the usable life left for the probe. Their time deployed is irrelevant given I can only assume it was less than the useable span of said probe. And unless the sensor was in an extremely harsh environment, I can’t imagine the RH chip within them are worn to any point of no return.

Of course some sensors we will have to buy new as that would be most logical. The barometric pressure sensor, thermistor probes, and GPS unit being of the many. But the money saved in the beginning with certain components will only help us in the long term when it comes time to upgrade.

So yes, we are making progress, slowly but surely. Will update this post when I hear back from CSI and go from there.

Edit: Campbell Scientific still does calibrate the HMP35C probes. Going this route will save us quite a bit financially. Then when the time comes we will upgrade accordingly.

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