Unidata – Water Depth Monitors
Unidata’s depth measurement instruments for borehole monitoring, recording river height and management of drainage systems
Unidata offers two water depth instruments: the 8007WDP Digital Water Level Recorder and the 6542 Hydrostatic Water Depth and Temperature Probe. Both use the hydrostatic pressure of water to measure water depths in various environments.
The two instruments differ in that the 8007WDP is self powered, and has an inbuilt Micrologger while the 6542 must be connected to a data logger on the surface. In addition, the 8007WDP is more accurate. Both instruments measure water temperature.
Typically the 8007WDP is used for measuring water level in boreholes while the 6542 is ideal for monitoring drainage levels, bore depth and river height. In water studies where more than water depth and temperature are required the 6542 may be more suitable since other instruments can be connected to the data logger on the surface.
The 8007WDP can measure water depths of 10m to 100m in standard ranges. Its includes a fully programmable 128k micrologger and lithium battery and can operate continuously for five years without service or recalibration. The 6542 provides accurate long term measurements of water depth from 0 to 20 metres.
Both instruments are housed in a rugged stainless steel casings but because it houses a battery and Micrologger, the 8007WDP is substantially larger. Both units use cables with a vent tube for barometric compensation and a Kevlar support member for longitudinal stability. The 8007WDP is supplied with a device that secures the cable to the borehole casing whereas in the case of the 6542, you must provide the means of securing the cable.
You can download data from these instruments via the RS-232 port of a computer or with the addition of some type of power supply such as a solar panel, battery and regulator, you can install a telemetry system.
A Note About Hydrostatic Probes
These probes use the hydrostatic pressure of water to measure depths in various environments. The hydrostatic pressure of water is dependent on the depth at which the water is measured and the atmospheric pressure. The maximum expected change in atmospheric pressure due to the change in weather in approximately 10kPa (100hPa) which is 1% of 1000kPa (100m head of water). The 1% is within the accuracy of a hydrostatic pressure transducer. Hence for this type of transducer it is important to relate the measurement against atmospheric pressure. For water depths of less than 100 metres (1000kPa) a gauge type transducer (Model 6542 or Model 7421) fitted with vented cable (e.g., Model 6600E or Model 7421X) is used. For depths greater than 100 metres you can use an absolute type transducer without vented cable.
