1. Equipment Specification: AWLR, FLOAT TYPE WITH CHART (SW) Version 2 10.004-1/3
10.004 AWLR, FLOAT TYPE WITH CHART (SW)
Approval Date: 28 July 2009 Version: 2
Purpose
The Auto-graphic Water Level Recorder (AWLR) is to make a continuous chart record of
water level versus time in rivers, lakes and reservoirs.
Conditions and requirements
• The instrument shall be of such a design that it operates reliably and accurately under the
prevailing environmental conditions.
• The instrument shall be easy to operate and maintain.
• The recorder shall generally comply with IS 9116-1979.
• All materials on the instrument exterior shall be non-corrosive.
• Materials in the interior shall be non-corrosive or corrosion resistant.
• The size of float and counter weight shall allow free movement in the stilling well; the
minimum inner diameter of the stilling well will be 0.5 m.
• The float and counter weight shall be suspended on a metal tape or a metal wire. Over the
full temperature range, the temperature effects on length should be insignificant, i.e. less
than 0.5 cm over the distance from the lowest water level to the pulley.
• The tape or wire shall be fitted with perforations or beads and matching sprockets or
cavities on the pulley wheel to prevent slip of the suspension.
• Errors due to friction in suspension and gearing should be less than 1 mm.
• Errors due to gearing backlash should be less than 1 mm.
• The chart paper should have perforations that match with the sprockets on the paper
transport mechanism.
• The chart paper shall be accurately guided to avoid change of zero due to traverse shift of
paper.
• The chart paper shall not be distorted, neither along the level axis nor along the time axis,
by moisture absorption due to the high humidity as encountered over the stilling well.
• The chart speed shall not change over time and shall not vary with the amount of paper
collected on the receiving roll (on a roll type recorder).
• The chart paper graduation shall match the instrument accuracy requirements, i.e.
graduation along the time and level axes shall be stable along the full paper size.
• The level graduation width shall precisely match with the plotting range; i.e. the pen
reversal points shall coincide with the edges of the pre-printed grid scale.
• The recorder zero shall be adjustable to the paper zero.
• The pen friction on the paper should be negligible and should not affect the level or time
accuracy.
• The recorder ink should be compatible with the environment and with the recording paper.
Smudging or dispersion should not occur.
• The recorder segment shall be well protected against the environment, only the pulley may
be directly exposed to the environment. The shaft running from the pulley to the recorder
segment should pass through a water barrier in the housing wall. Doors have to be fitted
with flexible seals. The seals should be of such material that they would not crumble, tear
or start leaking during the projected lifetime of the recorder. Gutters around the door are
required to avoid ingress of any hanging water when the door is opened.

2. Equipment Specification: AWLR, FLOAT TYPE WITH CHART (SW) Version 2 10.004-2/3
• The instrument shall be ready for addition of a shaft encoder with associated data logger
and batteries.
• The instrument shall be supplied with the required accessories, a set of gears for different
drum revolutions, and a set of pulleys to change the recording ratio.
• Operator’s and maintenance manuals, related to the type and model of the instrument,
shall be part of the delivery.
• Comprehensive operators and maintenance training for respectively field observers and
instrument specialists shall be part of the delivery.
• The proper functioning of each instrument shall be demonstrated at delivery.
Specifications
1. Sensor
sensor type float, pulley, counter weight
measuring range 0 to xx m water column (e.g. 0 to 10 or 0 to 20 m)
The Schedule of Requirements gives the numbers to be quoted for and the associated ranges
and it is attached to this document. The Bidder shall specify for the closest standard range of
the offered product with respect to the required measuring range. The quoted range shall be
equal or larger than the required range.
suspension perforated tape or beaded wire
pulley fitted with matching sprockets for perforated tape or matching
cavities for beaded wire
overall accuracy 0.005 m
The accuracy also includes the longitudinal properties of the float suspension and the shaft
encoder accuracy. The positioning of perforations/beads shall comply with the accuracy
requirement.
long term stability 0.002 m/year
Stability shall also cover the longitudinal tape/wire properties, e.g. elongation and creep of
the suspension tape/wire at the specified length.
reproducibility 0.001 m
2. Recorder
recording width 200 to 300 mm
pen reversal on both chart sides
chart range 1.25 or 2.5 m (before pen reversal)
overall accuracy 0.01 m, also including the effects of pen reversal
ink capacity >3 months, a fibre tip pen of the same capacity has preference
paper stability paper width may not vary more than 0.5 mm
level graduation printed level gradation accuracy should be better than the
equivalent of 1 mm water level on a 2.5 m scale. The lower
level sprocket wheel is the references for this specification.
time graduation printed time gradation should not vary more than 0.1 mm per
meter chart paper
chart speed 2, 5, 10 or 25 mm/h
moisture the effects of moisture content should be less than 0.01 m
water level change over 5 to 95 % relative humidity range on a
paper scale of 0 to 2.5 m.
Roll recorder
paper type strip chart on roll
chart length >10 m

3. Equipment Specification: AWLR, FLOAT TYPE WITH CHART (SW) Version 2 10.004-3/3
paper transport clock driven
OR
Drum recorder
paper type sheet on drum
chart length fully encompasses drum
paper transport clock driven, pen is float driven
OR
float (level) driven, pen is clock driven
3. Clock
Electrical clock
chart (pen) drive electrical
clock work quarts crystal controlled
protection against insects, moisture, dirt, etc
time keeping of clock 2 minutes per month or better
adjustment clock speed should be adjustable to paper graduation
power supply standard dry cell(s), C or D size
battery lifetime >3 month
OR
Mechanical clock
chart drive mechanical
clock work spring loaded
protection against insects, moisture, dirt, etc.
time keeping of clock <10 minutes per month under operational conditions
adjustment clock speed should be adjustable to paper graduation
clock autonomy >1 month, starting on fully wound spring
4. General
instrument lifetime >10 years of continuous operation
temperature range 0 to 60°C
humidity 100%
housing splash waterproof
Consumables
• chart paper rolls or sheets
• pens and ink
• batteries for the electrical clock
Remarks
The design for the stilling well and the housing of the recorder depends on the site-specific
conditions. The engineer in charge shall finalise the details on well and housing in
collaboration with the supplier.