Global Water WQ101, WQ201, WQ301, WQ401 Instruction Manual

Global Water

800-876-1172 • globalw.com

00-758
11/14/08

Global Water

Instrumentation, Inc.

11390 Amalgam Way

Gold River, CA 95670

T: 800-876-1172

Int’l: [phone], F: [phone]

Temperature Sensor: WQ101
pH Sensor: WQ201
Conductivity Sensor: WQ301
Dissolved Oxygen Sensor: WQ401
ORP/Redox: WQ600

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Global Water

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Congratulations on your purchase of the Global Water Water Quality
Sensor. This instrument has been quality tested and approved for
providing accurate and reliable measurements. We are confident that you
will find the sensor to be a valuable asset for your application. Should you
require assistance, our technical staff will be happy to help.

Table of Contents

I. Checklist • • • • • • • Page 3
II. Inspection

III. General Sensor Installation • • • • 4
IV. Temperature Sensor
V. pH Sensor
VI. Conductivity Sensor
VII. Dissolved Oxygen
VIII. ORP/Redox
IX. Maintenance
X. Troubleshooting
XI. Warranty

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XII. Appendix A: Calibration Procedures
XIII. Appendix B: 2 Wire Sensor Measurement Diagram
XIV. Appendix C: 3 Wire Sensor Measurement Diagram

* Copyright © Global Water Inst r umentation, Inc. 2008

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I. Sensor Checklist

a. Water Quality Sensor
b. Water Quality Sensor Manual

II. Inspection

a. Your water quality sensor was carefully inspected and certified by our

Quality Assurance Team before shipping. If any damage has occurred
during shipping, please notify Global Water Instrumentation, Inc. and
file a claim with the carrier involved.

Use the checklist to ensure that you have received everything needed
to operate the water quality sensor.

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III. Sensor Installation

General

a. Water quality sensors have many applications and therefore many

installation options. All the sensors are fully submersible and may be
suspended by their waterproof cables in the water to be monitored.

b. Do not install the water quality sensor in applications that contain

solvents. Over time, many solvents can deteriorate the cable and the
sensing element.

c. Install your water quality sensor so that it is easily accessible for

calibration purposes. You may need to remove and reinstall it in the
future, so plan ahead!

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d. The sensors will not function correctly if mud, silt, leaves, or garbage

buries them. The pH, Dissolved Oxygen, and ORP/Redox sensors will
fail if they are left out of the water for extended periods of time. Install
the sensor in a way that will avoid these conditions.

e. All Global Water water quality sensors produce a 4-19 mA output

signal. 4-19 mA is an industrial standard signal for process control
monitoring. Most PLCs (Programmable Logic Controller), RTUs
(Remote Telemetry Unit), and data acquisition systems accept this
signal directly. If the system only accepts voltage signals, the sensor
output must be converted to a voltage signal by reading the voltage
across a precision resistor in series with the signal wire. Since Ohms
Law states that V = IR, if the 4-19 mA signal is dropped across a 250
ohm resistor, the output will be 1 to 4.75 volts DC. If the 4-19 mA
signal is dropped across a 125 ohm resistor, the output will be halved
to 0.5 to 2.375 VDC. The 4-19 Ma signal wire is connected to the
datalogger voltage input terminal. The resistor is placed between this
input and the ground terminal of the datalogger’s battery. The power
(or voltage to the sensor) must be connected to positive battery
terminal of the datalogger.

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f. The sensors may be pulsed on or turned on by the logging system

prior to taking a reading. Use a warm up time appropriate to the water
quality sensor you are using to assure that the sensor is fully on. The
sensors can run continuously for real time applications. Each sensor
draws between 4 and 19mA depending on whether the sensor is
reading at the minimum or maximum of its range.

Groundwater
g. Sensors may be suspended in 2” monitoring wells near the well

screen. Several sensors may be suspended in the same well by
staggering the sensors one foot apart.

Surface Water
h. Sensors may be submerged at the monitoring point and hung from

their cables. It is recommended to protect the sensors inside a 4” PVC
drainpipe that will act as a protective stilling well. Put a cap on the
bottom end of the pipe to allow easy water flow past the sensors.
Drop the sensor until it touches the bottom of the stilling well and then
pull it up slightly and secure the cable.

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IV. Temperature Sensor

a. Temperature sensor specifications.

Output: 4-19mA
Range: -50° C to + 50° C
Accuracy: ±0.2° F or ±0.1° C
Operating Voltage: 10-36VDC
Current Draw: Same as sensor output.
Warm Up Time: 5 seconds minimum
Operating Temperature: -50°C to +100°C
Size of Probe: 3/4" diameter x 4 1/2" long
Weight: 1/2 lb.

b. The sensor is a two-wire sensor using the red wire for power and the

black wire for the output signal. Warning: Always connect the
sensor with the power turned off.

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c. The temperature sensor may be stored without any special provisions.

Place the sensor inside a bag to keep the sensor clean and store on a
shelf or hang it on a wall.

d. To check the temperature sensor calibration you will need:

1 thermometer
3 containers of water
1 power supply
1 current meter
Connecting wires as necessary

Connect the sensor to the power supply and current meter in
the following way. Attach the black wire to the positive input of the
current meter. Connect the ground terminal of the power supply to the
ground of the current meter. Attach the red wire to the positive
terminal of the power supply. See Appendix B. Warning: Always
connect the sensor with the power turned off.

See Appendix A for the temperature calibration worksheet.

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V. pH Sensor

a. pH sensor specifications.

Output: 4-19mA
Range: 0-14 pH
Accuracy: 2% of full scale
Operating Voltage: 10-36VDC
Current Draw: 16.6 mA plus sensor output
Warm Up Time: 3 seconds minimum
Operating Temperature: -5° to +55°C
Pressure Rating: 0-100 psi
Size of Probe: 1 1/4" diameter x 10" long
Weight: 1 lb.

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b. The sensing element is covered with a protective cap while at the

Global Water facility to prevent the sensor from becoming damaged.
This cap must be removed prior to sensor installation or the readings
will be in error. To remove the cap, remove the protective shield and
remove the rubber cap covering the sensing element. Replace the
protective shield. Note: Save the cap for future use.

c. This sensor has a removable sensing electrode. If the sensor is

reading incorrectly, after following the basic maintenance steps, the
electrode should be removed and the metal contacts cleaned. If this
does not improve the sensor’s results the electrode should be
replaced. To remove the sensing electrode loosen the set screw
holding the sensor shield and remove the shield from the sensor.
Unscrew the sensing electrode from the sensor housing. Clean the
metal contacts of the electrode with a clean cloth. If the electrode is
replaced with a new electrode the sensor must be recalibrated to work
correctly.

d. The pH sensor is a three-wire sensor. Three wire sensors use the red

wire for positive voltage, the white wire for the output signal, and the
black wire for ground. Warning: Always connect the sensor with
the power turned off.

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e. The pH sensor must be stored where the sensing element remains wet

or the sensing element will be damaged. It can be stored in a
container of clean water or a wet sponge can be placed inside the
protective cap shipped with the sensor. Place the cap over the
sensing element to keep it wet. The sensor can then be stored on a
shelf or hung on a wall.

f. The pH value of a substance is directly related to the ratio of hydrogen

ion (H+) and Hydroxyl ion (OH-) concentrations. If H+ is greater than
OH-, the solution is acidic, i.e., the pH value falls in the 0 to 7 range. If
the OH- is greater than the H+, the material is basic with a pH value in
the 7 to 14 range. If equal amounts of H+ and OH- ions are present,
the material is neutral with a pH value of 7.

The pH electrode can be thought of as a battery whose voltage
changes as the pH of the solution in which it is inserted changes. It
consists of two basic parts: 1) a Hydrogen ion-sensitive glass bulb,
and 2) a reference electrode. The special glass of the sensitive bulb
has the ability to pass H+ i.e., it is said to be H+ sensitive. This ability
allows the H+ inside the bulb to be compared to the H+ outside of the
bulb, and a voltage to be developed that is related to the difference.
The bulb then is a half-cell that needs a reference voltage in order to
function.

The voltage produced by the complete probe is a linear function of
pH, generally about 60 mV per pH unit. For example, at 7.00 pH the
probe produces zero volts while at 6.00 pH it produces +60 mV. If the
voltage had been negative it would indicate that the solution had a
value of 8.00 pH.

A buffer solution is a solution with a well-defined pH value and has
the ability to resist changes in pH. These characteristics are well
suited to the standardization of pH measuring systems. Buffers are
available in a wide range of pH values and come either in pre-mixed
liquid form or as convenient dry powder capsules. When selecting
buffers for use with your particular system, a value should be chosen
nearest to that of the sample being measured.

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