Geokon 4675LV User manual

Instruction Manual
Model 4675LV
Weir Monitor
No part of this instruction manual may be reproduced, by any means, without the written consent of
Geokon, Inc The information contained herein is believed to be accurate and reliable. However,
Geokon, Inc. assumes no responsibility for errors, omissions or misinterpretation. The information
herein is subject to change without notification.
Copyright © 1991, 2004, 2006, 2011, 2012, 2013 by Geokon, Inc.
(Doc Rev H, 6/13)

Warranty Statement
Geokon, Inc. warrants its products to be free of defects in materials and workmanship,
under normal use and service for a period of 13 months from date of purchase. If the
unit should malfunction, it must be returned to the factory for evaluation, freight
prepaid. Upon examination by Geokon, if the unit is found to be defective, it will be
repaired or replaced at no charge. However, the WARRANTY is VOID if the unit
shows evidence of having been tampered with or shows evidence of being damaged
as a result of excessive corrosion or current, heat, moisture or vibration, improper
specification, misapplication, misuse or other operating conditions outside of Geokon's
control. Components which wear or which are damaged by misuse are not warranted.
This includes fuses and batteries.
Geokon manufactures scientific instruments whose misuse is potentially dangerous.
The instruments are intended to be installed and used only by qualified personnel.
There are no warranties except as stated herein. There are no other warranties,
expressed or implied, including but not limited to the implied warranties of
merchantability and of fitness for a particular purpose. Geokon, Inc. is not responsible
for any damages or losses caused to other equipment, whether direct, indirect,
incidental, special or consequential which the purchaser may experience as a result of
the installation or use of the product. The buyer's sole remedy for any breach of this
agreement by Geokon, Inc. or any breach of any warranty by Geokon, Inc. shall not
exceed the purchase price paid by the purchaser to Geokon, Inc. for the unit or units,
or equipment directly affected by such breach. Under no circumstances will Geokon
reimburse the claimant for loss incurred in removing and/or reinstalling equipment.
Every precaution for accuracy has been taken in the preparation of manuals and/or
software, however, Geokon, Inc. neither assumes responsibility for any omissions or
errors that may appear nor assumes liability for any damages or losses that result
from the use of the products in accordance with the information contained in the
manual or software.

Contents
SPECIFICATIONS.................................................................................................................................................1
2. INSTALLATION PROCEDURES....................................................................................................................2
2.1. PRELIMINARY CHECKS ....................................................................................................................................2
2.2 INSTALLATION..................................................................................................................................................2
3. TAKING READINGS.........................................................................................................................................4
3.1. OPERATION OF THE GK-403 READOUT BOX...................................................................................................4
3.2. OPERATION OF THE GK404 READOUT BOX....................................................................................................5
3.3. OPERATION OF THE GK405 READOUT BOX....................................................................................................5
3.4. MEASURING TEMPERATURES..........................................................................................................................6
4. DATA REDUCTION ..........................................................................................................................................7
4.1 DETERMINATION OF WATER ELEVATION.........................................................................................................7
4.2 CORRECTIONS FOR TEMPERATURE CHANGES...................................................................................................9
5. MAINTENANCE ..............................................................................................................................................10
5.1 MOISTURE TRAP.............................................................................................................................................10
5.2 WEIGHT MAINTENANCE .................................................................................................................................10
5.3 SENSOR ..........................................................................................................................................................11
6. TROUBLE SHOOTING...................................................................................................................................11
APPENDIX 1 THERMISTOR LINEARIZATION USING STEINHART AND HART LOG EQUATION12

LIST of FIGURES, TABLES and EQUATIONS
FIGURE 1. STILLING -WELL SUPPORTS.................................................................................................................... 3
FIGURE 2GK405 READOUT UNIT ............................................................................................................................ 6
FIGURE 3TYPICAL CALIBRATION SHEET................................................................................................................... 8
FIGURE 4. DENSITY P OF PURE WATER AS A FUNCTION OF TEMPERATURE AND PRESSURE INTENSITY.BY
PERMISSION FROM FLUID MECHANICS FOR HYDRAULIC ENGINEERS,BY HUNTER ROUSE,COPYRIGHT
1938, MCGRAW-HILL BOOK COMPANY,INC..................................................................................................10

1
Specifications
Model No.
4675LV
Range
mm1150, 300, 600, 1500
Accuracy2
±0.1% F.S.
Temperature Range
3-30°to +80°C
Frequency Range
1400-3500Hz
Materials:
Sensor and
weight:
Stilling Well:
Stainless steel
PVC standard, stainless steel
(optional)
Cable
4-Conductor, 22 gage PVC jacket
Sensor
Diameter - 1.00”
Length - 8.5”
1Other ranges available on request
2Accuracy achieved by using a polynomial expression rather than a linear coefficient
3Using anti-freeze solution can extend the range below 0°C. The system requires
calibration with the solution being used.

2
1. Introduction______________________________________________________
The Geokon Model 4675LV Weir Monitor is designed for the measurement of water
levels in streams, weirs, flumes, etc., where accurate measurements of very small
water level changes are required. The unit consists of a vibrating wire from which is
suspended a hanging cylindrical weight partially submerged in the water. As the water
level rises and falls, the buoyancy forces acting on the weight change causing
changes in the tension and vibrational frequency in the vibrating wire. Level changes
of as little as .001” can be measured. Ranges of up to 10’ are available.
2. Installation Procedures _____________________________________________
2.1. Preliminary Checks
Before installing the weight cylinder, there is an orange colored spacer which
lies between the base of the sensor and the nut on the hook assembly, this
needs to be removed. (This releases the tension in the sensor wire –put there as a
safety precaution to protect the sensor from damage during shipment.)
The gage and weight assembly can now be checked out on site by connecting the
sensor to the readout system and measuring the output of the sensor with the weight
hanging from it in air. The readings [in Readout box channel “B”] should coincide
within about 200 digits of the factory reading in air shown on the calibration sheet. Be
sure that the sensor is held firmly and allow the system to stabilize (no swinging of the
weight). Detach the weight after this preliminary check. Always handle with great
care to prevent breakage.
2.2 Installation
If the 4675LV is used in a weir box, a stilling-well is required. The stilling-well is
provided by Geokon, in the form of a slotted, 3 inch or 4 inch PVC pipe. This stilling
well must be installed in a vertically plumb position in an area where there is little
turbulence and positioned in such a way that the bottom of the weight is slightly
lower than the tip of the V notch, It is important that the well be vertical, because
any friction from the weight rubbing along the well will influence the sensor output
The installation is made by using two pipe-straps to hold the stilling well in place. Two
spacer bars are provided to hold the stilling well away from the wall so that the stilling

3
well cap can be removed and replaced as necessary. For concrete weir boxes 4 Rawl
plugs are provided. Mark out the position for four bolt holes, (see Figure 1), and drill a
½ inch (12mm) diameter hole 2 inch (50mm) deep at each location. (The spacer bar
can be used to help locate the hole spacing properly). A 3/8 Rawl plug (four provided)
is installed in each hole, using the installation tool provided. The Rawl plug is first
placed in the hole and tapped flush with the surface. Then place the installation tool
inside the Rawl plug and set the anchor by means of several sharp hammer blows.
The PVC slotted tubing has a bottom plug at its lower end, which can now be
cemented in place using PVC cement. (It is left loose in case the PVC pipe needs to
be shortened a little due to space limitations). Use the four 3/8-16 bolts provided to
bolt the stilling well to the wall of the weir box using the pipe-strap and spacer bars.
Figure 1. Stilling -Well Supports.

4
Check that the sensor is reading then push it inside the Swagelok fitting in the pipe
cap and tighten the Swagelok one full turn after finger tight. Leave about one inch of
the sensor protruding from the Swagelok. Carefully attach the weight to the eyebolt on
the base of the sensor and lower the assembly into the stilling well until the pipe cap
sits firmly on top of the pipe.
The yellow vented readout cable can now be extended to a local readout location
where an optional terminal box can be used to enclose the end of the yellow vented
cable and the vent line moisture trap. If the readout location is remote from the weir
location then a blue un-vented cable can be used between the terminal box containing
the moisture trap and the readout location.
3. Taking Readings___________________________________________________
3.1. Operation of the GK-403 Readout Box
The GK-403 can store gage readings and also apply calibration factors to convert
readings to engineering units, ie. inches or millimeters. Consult the GK-403
Instruction Manual for additional information on Mode "G" of the Readout. The
following instructions will explain taking gage measurements using Mode "B".
Connect the Readout using the flying leads or in the case of a terminal station, with a
connector. The red and black clips are for the vibrating wire transducer, the white and
green clips are for the thermistor and the blue for the shield drain wire.
1. Turn on the Readout. Turn the display selector to position "B". Readout is in
digits.
2. Turn the unit on and a reading will appear in the front display window. The last
digit may change one or two digits while reading. Press the "Store" button to
record the value displayed. If the no reading displays or the reading is unstable
see section 5 for troubleshooting suggestions. The thermistor will be read and
output directly in degrees centigrade.
3. The unit will automatically turn its-self off after approximately 2 minutes to
conserve power.

5
3.2. Operation of the GK404 Readout Box
The GK-404 is a palm sized readout box which displays the Vibrating wire value and
the temperature in degrees centigrade.
The GK-404 Vibrating Wire Readout arrives with a patch cord for connecting to the
vibrating wire gages. One end will consist of a 5-pin plug for connecting to the
respective socket on the bottom of the GK-404 enclosure. The other end will consist
of 5 leads terminated with alligator clips. Note the colors of the alligator clips are red,
black, green, white and blue. The colors represent the positive vibrating wire gage
lead (red), negative vibrating wire gage lead (black), positive thermistor lead (green),
negative thermistor lead (white) and transducer cable drain wire (blue). The clips
should be connected to their respectively colored leads from the vibrating wire gage
cable. Use the POS (Position) button to select position Band the MODE button to
select Dg (digits).
Other functions can be selected as described in the GK404 Manual.
The GK-404 will continue to take measurements and display the readings until the
OFF button is pushed, or if enabled, when the automatic Power-Off timer shuts the
GK-404 off. The GK-404 continuously monitors the status of the (2) 1.5V AA cells, and
when their combined voltage drops to 2V, the message Batteries Low is displayed on
the screen. A fresh set of 1.5V AA batteries should be installed at this point.
3.3. Operation of the GK405 Readout Box
The GK-405 Vibrating Wire Readout is made up of two components:
•the Readout Unit, consisting of a Windows Mobile handheld PC running the GK-405
Vibrating Wire Readout Application
•the GK-405 Remote Module which is housed in a weather-proof enclosure and connects
to the vibrating wire sensor by means of:
1) Flying leads with alligator type clips when the sensor cable terminates in bare wires or,
2) by means of a 10 pin connector..
The two components communicate wirelessly using Bluetooth®, a reliable digital
communications protocol. The Readout Unit can operate from the cradle of the Remote
Module (see Figure 2) or, if more convenient, can be removed and operated up to 20 meters
from the Remote Module

6
Figure 2 GK405 Readout Unit
For further details consult the GK405 Instruction Manual.
3.4. Measuring Temperatures
Each Vibrating Wire Convergence Meter is equipped with a thermistor for reading
temperature. The thermistor gives a varying resistance output as the temperature
changes. Usually the white and green leads are connected to the internal thermistor.
The GK-403, GK-404 and GK-405 readout boxes will read the thermistor and display
temperature in °C automatically.
However, if an ohmmeter is used
1. Connect the ohmmeter to the two thermistor leads coming from the convergence
meter. (Since the resistance changes with temperature are so large, the effect of
cable resistance is usually insignificant.)
2. Look up the temperature for the measured resistance in Table B-1 (Appendix B).
Alternately the temperature could be calculated using Equation B-1 (Appendix B).
For example, a resistance of 3400 ohms is equivalent to 22° C. When long cables
are used the cable resistance may need to be taken into account. Standard 22
AWG stranded copper lead cable is approximately 14.7Ω/1000' or 48.5Ω/km,
multiply by 2 for both directions.

7
4. Data Reduction ____________________________________________________
4.1 Determination of Water Elevation
Each type of weir, depending on its type, shape and size has an equation relating the
volume of fluid passing over it to the height of water, H, passing over the weir.
The change in height of the water is directly proportioned to the change in output of
the transducer. The following formula applies for the determination of the change in
water height.
ΔH = (R1– R0) G
At the time that the initial reading R0is taken it is necessary to measure accurately as
possible the difference in elevation between the surface of the water in the weir box
and the tip of the weir. If the weir plate is graduated just record the initial water level
as indicated, Call this difference in elevation ΔE.Then
H = (R1– R0) G + ΔEinches or mm
Where H is the height of water above the tip of the weir,
R0is the initial reading
R1is the subsequent reading
G is the calibration factor in the height units /digit shown on the calibration sheet
Alternatively, from the initial reading RItaken when the measured water height is ΔE
inches, it is possible, using the gage factor, G, to calculate Ro, the reading equivalent
to the water level at the tip of the V notch, For instance if RI= 6500 and ΔE= 5.2
inches, and G= - 0.001981 inches then Ro= 6500 + 5.2/0.001981= 9125 and
H = G(RI -9125)
Another method, if at all possible, is to adjust the height of water so that water just
trickles over the V notch tip, and then take the Roreading.

8
Figure 3 Typical Calibration Sheet

9
4.2 Corrections for Temperature Changes
The vibrating wire sensor itself is insensitive to temperature changes within the normal
operating range. The system, however, is not entirely unaffected by changes in water
temperature which influence the density and therefore, the buoyancy of the fluid. The
influence is relatively minor and can be accounted for to some degree by measuring
the water temperature and making density corrections. Alternatively, two sensors can
be used, one of which is completely submerged at all times and whose output can be
used to make corrections for the other sensor. This technique is not fool proof either
since the water may have temperature gradients which the submerged sensor may or
may not intersect. A temperature/density curve for water is shown in Figure 1. As can
be seen from the data the density of the water changes very little in the normal
operating range of the sensor. The following equation is used to correct for
temperature/density changes:
∆H = (R0) G /(1- 0.0002T0) - (R1) G /(1- 0.0002T1)
Where T is the water temperature in °C.

10
Density and Compressibility
Density is defined as the mass per unit volume, and it depends upon the temperature
and pressure intensity. The density of pure water is given in Figure 4 below.
Figure 4. Density p of pure water as a function of temperature and pressure
intensity. By permission from Fluid Mechanics for Hydraulic Engineers, by
Hunter Rouse, copyright 1938, McGraw-Hill Book Company, Inc.
5. Maintenance ______________________________________________________
5.1 Moisture Trap
The vibrating wire sensor has a vent tube to prevent loading on the sensor due to
changes in atmosphere pressure, and the moisture trap on the vent line requires
periodic changing of the desiccant capsules. The frequency of this is dependent on
weather conditions, but three to six months is a normal period.
5.2 Weight Maintenance
Since the weight is assumed to be of constant mass, it is important that it be kept
clean and free of encrustation, algal growth, etc. Periodic observation should be made
and this can coincide with the moisture trap maintenance.

11
5.3 Sensor
Maintenance of the sensor itself is confined to periodic checks of cable connections
and maintenance of terminals. The transducers themselves can not be opened for
inspection.
6. Trouble Shooting __________________________________________________
If a unit fails to read, the following steps should be taken:
1. Check the coil resistance. Nominal coil resistance is 180 Ω±10 plus cable
resistance
(22 gage copper = approximately 15 Ωper 1000 feet).
a.) If the resistance is high or infinite, a cut cable must be suspected.
b.) If the resistance is low or near zero, a short must be suspected.
c.) If resistance’s are within nominal and no readings are obtainable on any
transducer, the readout is suspect
and the factory should be consulted.
d.) If all resistance’s are within nominal and no readings are obtainable on any
transducer, the readout is
suspect and the factory should be consulted.
2. If cuts or shorts are located, the cable may be spliced in accordance with
recommended procedures.

12
Appendix 1 Thermistor Linearization using Steinhart and Hart Log
Equation
Thermistor Type: YSI 44005, Dale #1C3001-B3, Alpha #13A3001-B3
Basic Equation:
TA B LnR CLnR
=
++
−
12732
3
() ( ).
where:
T =Temperature in °C
LnR =Natural Log of Thermistor Resistance
A =1.4051 ×10-3
B =2.369 ×10-4
C =1.019 ×10-7
Note: Coefficients calculated over −50°to +150°C span.
Resistance versus Temperature Table
Ohms
Temp
Ohms
Temp
Ohms
Temp
Ohms
Temp
Ohms
Temp
201.1K
-50
16.60K
-10
2417
+30
525.4
+70
153.2
+110
187.3K
-49
15.72K
-9
2317
31
507.8
71
149.0
111
174.5K
-48
14.90K
-8
2221
32
490.9
72
145.0
112
162.7K
-47
14.12K
-7
2130
33
474.7
73
141.1
113
151.7K
-46
13.39K
-6
2042
34
459.0
74
137.2
114
141.6K
-45
12.70K
-5
1959
35
444.0
75
133.6
115
132.2K
-44
12.05K
-4
1880
36
429.5
76
130.0
116
123.5K
-43
11.44K
-3
1805
37
415.6
77
126.5
117
115.4K
-42
10.86K
-2
1733
38
402.2
78
123.2
118
107.9K
-41
10.31K
-1
1664
39
389.3
79
119.9
119
101.0K
-40
9796
0
1598
40
376.9
80
116.8
120
94.48K
-39
9310
+1
1535
41
364.9
81
113.8
121
88.46K
-38
8851
2
1475
42
353.4
82
110.8
122
82.87K
-37
8417
3
1418
43
342.2
83
107.9
123
77.66K
-36
8006
4
1363
44
331.5
84
105.2
124
72.81K
-35
7618
5
1310
45
321.2
85
102.5
125
68.30K
-34
7252
6
1260
46
311.3
86
99.9
126
64.09K
-33
6905
7
1212
47
301.7
87
97.3
127
60.17K
-32
6576
8
1167
48
292.4
88
94.9
128
56.51K
-31
6265
9
1123
49
283.5
89
92.5
129
53.10K
-30
5971
10
1081
50
274.9
90
90.2
130
49.91K
-29
5692
11
1040
51
266.6
91
87.9
131
46.94K
-28
5427
12
1002
52
258.6
92
85.7
132
44.16K
-27
5177
13
965.0
53
250.9
93
83.6
133
41.56K
-26
4939
14
929.6
54
243.4
94
81.6
134
39.13K
-25
4714
15
895.8
55
236.2
95
79.6
135
36.86K
-24
4500
16
863.3
56
229.3
96
77.6
136
34.73K
-23
4297
17
832.2
57
222.6
97
75.8
137
32.74K
-22
4105
18
802.3
58
216.1
98
73.9
138
30.87K
-21
3922
19
773.7
59
209.8
99
72.2
139
29.13K
-20
3748
20
746.3
60
203.8
100
70.4
140
27.49K
-19
3583
21
719.9
61
197.9
101
68.8
141
25.95K
-18
3426
22
694.7
62
192.2
102
67.1
142
24.51K
-17
3277
23
670.4
63
186.8
103
65.5
143
23.16K
-16
3135
24
647.1
64
181.5
104
64.0
144
21.89K
-15
3000
25
624.7
65
176.4
105
62.5
145
20.70K
-14
2872
26
603.3
66
171.4
106
61.1
146
19.58K
-13
2750
27
582.6
67
166.7
107
59.6
147
18.52K
-12
2633
28
562.8
68
162.0
108
58.3
148
17.53K
-11
2523
29
543.7
69
157.6
109
56.8
149
55.6
150