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Model: 6541
Technical Specs |
Order Info
Float-operated instruments can be the most accurate way to monitor the level of a water surface. The new Unidata Model 6541 Precision Water Level Instrument can achieve an operating accuracy and resolution of 0.2mm. This accuracy is maintained for the service life of the instrument without calibration or maintenance, apart from battery changes. Each instrument has the range to monitor surface and underground waters, and the precision to monitor rainfall and evaporation.
This Model 6541 instrument supercedes the Unidata Model 6509 and 6531 instruments that have been the choice of experienced professionals at more than 1000 sites worldwide since introduction in 1985.
The instrument is normally connected to the water surface by a float system. As the water level changes, this rotates the input shaft on which is mounted an optical encoder. At installation the instrument is set to display the water level on its LCD screen.
The encoder is continuously monitored and the instrument tracks any water level changes. These changes update the LCD screen and the displayed reading can be recorded by an associated data logger.
The very low mechanical friction and intertia of the instrument produce data of high precision and accuracy. A replaceable battery pack powers the instrument for more than 1 year. The practical design and rugged construction ensure easy operation and a long service life.

| Range: |
Standard 0 to 65.5 metres. Switch to 13.1m or 65.5 feet. |
| Resolution: |
1.0mm, 0.2mm or 0.01 foot, depending on float pulley used. |
| Accuracy: |
Same as resolution with suitable float system. |
| Tracking: |
Up to 500mm/second. |
| Display: |
6-digit LCD |
| Temperature: |
-40°C to +60°C |
| Humidity: |
0-100%, non-condensing |
| Output: |
High speed serial signal UNIDATA HSIO standard. Options for SDI-12, 4-20mA and dual HSIO channels. Up to 8 instruments can be daisy chained. |
| Power: |
Internal Alkaline battery pack. Expected life exceeding 12 months. Exchange pack UNIDATA Model 6910A. External battery power 9-15VDC can be connected. |
| Cable: |
5 metres (supplied). Up to 30 metres may be used. |
| Size: |
180×275×140mm (W×H×D) |
| Weight: |
2.7kg, including battery |
| Construction: |
Exterior PVC, Aluminium and stainless steel. |
| Enclosure: |
Sealed PVC IP65. |

| Model |
Description |
Includes |
Requires |
| 6541-10 |
Water Level Instrument, 500mm pulley (1mm resolution), no battery |
6541A, 6541P/M500 |
6541D/M |
| 6541-11 |
Water Level Instrument, 500mm pulley (1mm resolution), Alkaline battery |
6541A, 6541P/M500, 6910A |
6541D/M |
| 6541-11/C |
Water Level Logger, 512K Micrologger, 500mm pulley (1mm resolution), Alkaline battery |
6541A, 6541L, 6541P/M500, 6910A |
6541D/M |
| 6541-21 |
Water Level Instrument, 1ft pulley, Alkaline battery |
6541A, 6541P/I12, 6910A |
6541D/I |
| 6541-30 |
Water Level Instrument, 100mm pulley (0.2mm resolution), no battery |
6541A, 6541P/M100 |
6541D/U |
| 6541-31 |
Water Level Instrument, 100mm pulley (0.2mm resolution), Alkaline battery |
6541A, 6541P/M100, 6910A |
6541D/U |
| 6541-41 |
Water Level Instrument, 5in pulley (0.01in resolution), Alkaline battery |
6541A, 6541P/I5, 6910A |
6541D/U |
| 6541A |
Precision Water Level Instrument, housing, LCD, no pulley, no battery |
| 6541C |
Counterweight 160g |
for 6541F float assemblies |
| 6541D/I |
Stainless steel beaded floatline, 3in spaces |
for 6541P/I12 pulley |
| 6541D/M |
Stainless steel beaded floatline, 125mm spaces |
for 6541P/M500 pulley |
| 6541D/U |
Stainless steel unbeaded floatline, 1mm dia |
for 6541P/M500 and 6541P/I12 pulleys |
| 6541E |
Stainless steel unbeaded floatline, 0.4mm dia |
for 6541P/M100 and 6541P/I5 pulleys |
| 6541F/115 |
115mmD×60mmL float assembly, cylinder |
for 150mm stillwell |
| 6541F/170 |
170mmD×85mmL float assembly, cylinder |
for 200mm stillwell |
| 6541F/200 |
200mmD float assembly, round |
for 250mm stillwell |
| 6541F/60 |
60mmD×170mmL float assembly, cylinder |
for 100mm stillwell |
| 6541F/90 |
90mmD×130mmL float assembly, ovoid |
for 120mm stillwell |
| 6541F/EP |
170mmD×85mmL float and endless return pulley |
| 6541L |
Micrologger Assembly, 512K, 1 counter, 2 analog, SDI-12, HSIO |
| 6541M |
Mounting Plate Adaptor (install 6541 into 6509 mounting) |
| 6541O |
Offset pulley kit |
suits 4in boreholes |
| 6541P/I12 |
Pulley, 1ft circ., beaded, 0.01ft res. |
suits 6541D/I or 6541D/U line |
| 6541P/I5 |
Pulley, 5in circ., unbeaded, 0.01in res. |
suits 6541D/U line |
| 6541P/M100 |
Pulley, 100mm circ., unbeaded, 0.2mm res. |
suits 6541D/U line |
| 6541P/M500 |
Pulley, 500mm circ., beaded, 1mm res. |
suits 6541D/M or 6541D/U line |
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