Hydrology Field Methods

Environmental Measurements

Datalogger Voltage

Use the P10 command
Never let the battery voltage fall below 12 volts

Temperature Measurement

Temperature internal to the datalogger is determined using the P17 command
Temperature external to the datalogger can be measured using a thermocouple or a thermistor.
- Thermocouple
  - A thermocouple is composed of two wires (e.g., constantin-copper) that are connected in series at a junction.
  - The voltage across the junction is a function of the temperature at the junction.
  - The higher the temperature, the greater the voltage.
  - Measuring the voltage yields an estimate of the temperature of the junction.
  - This ignores the temperature of the other junctions internal to the datalogger.
  - There are actually two junctions, one at the external junction, and the other at the internal junction.
  - The actual temperature is the temperature of the internal junction, minus the temperature difference between the two junctions.
- Thermistor
  - A thermistor is a precision resistor that changes resistance with temperature.
  - Because the datalogger does not measure resistance, we use a bridge to determine the resistance.

Precipitation Measurement

Tipping Bucket
- A tipping bucket is used to collect rainfall in units of either 0.01", 1 mm, or 0.1 mm.
- A pulse counter is used to totalize the number of tips of the bucket.

Water Level Measurements

Pressure Transducers
- Changes in water level increase the pressure at a given depth.
- A pressure change causes a change in resistance in a sensor
- The change in resistance is converted to a change in voltage
- The datalogger measures the change in voltage

Evaporation/Precipitation

A water level sensor can be used to monitor changes in a container
Increases in depth correspond to rainfall
Decreases in depth correspond to evaporation

Datalogger Guide

Command 01: 02: 03: 04: 05: 06: 07: 08:

P10 Battery Voltage Loc

P17 Internal Temperature Loc

P7 Half-Bridge Reps Range Channel ExChan Ex mV Loc Mult Offset

P6 Full Bridge Reps Range Channel ExChan Ex mV Loc Mult Offset

P1 SE Voltage Reps Range Channel Loc Mult Offset

P2 Diff Voltage Reps Range Channel Loc Mult Offset

P3 Pulse Reps Channel Config Loc Mult Offset

Measurement Accuracy

Range Fast Slow 60 Hz reject

± 2.5 mV 1 11 21

± 7.5 mV 2 12 22

± 25 mV 3 13 23

± 250 mV 4 14 24

± 2500 mV 5 15 25

Assignment: Environmental Measurements

Program a datalogger to collect the following information in the laboratory
- Battery voltage (P10 instruction)
- Internal temperature (P17 instruction)
- Air temperature using a thermistor (P7 instruction)
- Water levels using a pressure transducer (P6 instruction)
- Precipitation using a tipping bucket (P3 instruction)
Record data every 10 minutes for each of the above variables (P92 instruction)
- Average (P71 instruction) or total (P72 instruction)
- Minimum (P74 instruction)
- Maximum (P73 instruction)
- Standard deviation (P82 instruction)
Move the equipment to the roof of Building 3
- Place the datalogger in a water-tight container
- Install the water level sensor in the pan.
- Continue to record data every ten minutes for three days.

Command		01:	02:	03:	04:	05:	06:	07:	08:
P10	Battery Voltage	Loc
P17	Internal Temperature	Loc
P7	Half-Bridge	Reps	Range	Channel	ExChan	Ex mV	Loc	Mult	Offset
P6	Full Bridge	Reps	Range	Channel	ExChan	Ex mV	Loc	Mult	Offset
P1	SE Voltage	Reps	Range	Channel	Loc	Mult	Offset
P2	Diff Voltage	Reps	Range	Channel	Loc	Mult	Offset
P3	Pulse	Reps	Channel	Config	Loc	Mult	Offset

Range	Fast	Slow	60 Hz reject
± 2.5 mV	1	11	21
± 7.5 mV	2	12	22
± 25 mV	3	13	23
± 250 mV	4	14	24
± 2500 mV	5	15	25