Hydrology Field Methods
Datalogger Overview
General Information:
- Dataloggers allow the remote collection and processing of data, thus increasing dramatically the precision, accuracy and frequency of field data.
- It is very easy to improperly collect data because of poor calibration and understanding of the behavior of automated equipment.
- A fundamental understanding of field equipment operation is essential.
- This section summarizes the basic workings of the Campbell Scientific, CR-10 datalogger.
- Check out the Campbell Scientific website at www.campbellsci.com
Power Supply:
- Batteries
- Datalogger operation requires a power source.
- This is normally supplied by a 12-volt DC (direct current) battery.
- It is important to attach the negative lead (or current ground) to the datalogger lead first, and then attach the positive lead of the battery to the datalogger (check this in manual!).
- The battery is never exactly 12 volts, varying from a maximum of 13.7 during charging to a low of less than 10 volts when fully discharged.
- The actual voltage is a measure of the amount of charge left on the battery.
- The ground voltage on a battery or in the datalogger is never a zero voltage.
- Battery voltages are relative to a ground, which may be unstable.
- Grounding of a battery can be dangerous.
- The amount of power in a battery may or may not be a function of the size of the battery.
- Some large batteries are intended to deliver a small amount of power over a short time period, while a smaller battery may deliver more total power over a longer time period.
- The supply voltage can be monitored using the P10 instruction.
- Recharging Batteries
- Batteries should be recharged when they drop below approximately 12 volts.
- Batteries should be recharged slowly, using a DC trickle charger.
- 12-volt AC power supplies will not recharge a DC battery.
- Solar panels can be used to trickle charge the battery.
- Too much power at one time can damage the battery.
- Some solar panel systems have a power restrictor that prevents overcharging
- Switched and Unswitched Power
- Unswitched 12-volts
- The datalogger can pass the supply voltage to another piece of equipment.
- The supply voltage is not controlled, and is dependent on the power supply voltage.
- The unswitched 12-volts is always on.
- Switched 12 volts
- The datalogger can provide switched 12 volts, which means that the power coming into the
datalogger can be delivered to another piece of equipment depending upon the status of a
datalogger instruction.
- Unswitched 5 volts
- The datalogger provides a precision 5000 mV (millivolt) power source.
- Switched variable power
- A precision power source can also be switched, up to a maximum 2500 mV.
Datalogger Programming
- Input channels
- There are twelve voltage input channels on the datalogger.
- The channels can be configured as a single-ended (SE) or a double-ended (DE) measurement.
- A single-ended measurement is the difference in voltage between the channel and the ground.
- A single-ended measurement can not exceed ± 2500 mV.
- A double-ended measurement is the voltage difference between two channels.
- Neither end of a double-ended measurement can exceed ± 2500 mV.
- Intermediate Storage
- Used to collect data for each sampling interval.
- The sampling interval can be set to (just about) any frequency.
- A set of instructions are used to tell the datalogger which operation to execute, which channel the data will be entering the datalogger, and which intermediate storage location will be used to display the data.
- Final storage
- Used to summarize intermediate data.
- The final storage is reported less frequently than the sampling interval.
- The final storage can be the total, average, extreme or standard deviation of the intermediate observations.