Short guide explaining how wire a pH and conductivity sensor to a Zeno 3200 data logger. The models mentioned may not be manufactured anymore at this time.

1. 1
Connecting a 4-20mA pH and Conductivity Probe to a Zeno Datalogger
This is how to install a WQ201 pH Sensor from Global Water Instrumentation
(http://www.globalw.com/) The job is similar for the WQ301 Conductivity Sensor (0-
10000 Micro Siemens (micro mhos per cm).
Tools and Materials: Screwdriver, wire strippers, some additional short pieces of wire of
similar gauge to probes, high tolerance resistor from Coastal Environmental (25.0Ω, .1%,
current sense resistor for 4 - 20 mA applications (CES P/N 1008Z) ). Any resistor from
Radio Shack with lower tolerances will not work.
Each of these is a 4-20mA sensor, so each one will take up a “+” and a “-“ on the Zeno
3200 datalogger. So, only a maximum of seven 4-20mA can be wired to a Zeno.
1. Begin by placing the resistor across a chosen channel. A resistor has no polarity,
so it does not matter which way it is installed. In this case, let us start with
Channel 7. Each probe has a red wire, white wire, and a black wire.
2. Connect the red wire to the 12 V SW’D terminal (upper right hand terminal). If
choosing a terminal other than Channel 7, it may be necessary to strip some wire
off of the cable so the terminal can be reached or twist an additional length of
wire.
3. Connect the white wire to the “+” terminal of Channel 7. Connect the black wire
to the “-“ terminal. Another piece of wire of similar gauge needs to be connected
from the “-“ terminal to any of the “GND” terminals on the Zeno 3200.
After wiring, the next step is to program the Zeno 3200 to record the pH or conductivity
values properly and calibrate the sensor.
Programming the Zeno 3200
Make sure the Zeno 3200 is beginning with a blank slate under the Zeno Program Menu.
Refer to the Zeno manual for clearing the sensor records, process records, and data
records. The following pages show exactly what to enter after wiring the probe to the
datalogger.
The section after describes how to calibrate the pH sensor and enter the proper values.

2. 2
SENSOR MENU
ITEM DATA COMMAND ENTERED
Item 1: Sensor Type code = 3 c1/3
Item 2: Sensor Name = current c2/current
Item 3: Sensor Input Channel = 1 c3/1
Item 4: Analog Channel Gain = 1 DEFAULT
Item 5: Analog Channel Attenuation = 1 DEFAULT
Item 6: Switched Power code = 31
C6/31
Item 7: Sensor Excitation Voltage = 0 DEFAULT
Item 8: Switched Excitation Return Code = 0 DEFAULT
Item 9: Sensor Warm up Time = 3 C9/3
Item 10: Sensor Sample Count = 1 DEFAULT
Item 11: Maximum Sensor Readings = 0 DEFAULT
Item 12: Sensor Timing Loop = 2 c12/2
Item 13: Conversion Coefficient A = 0 DEFAULT
Item 14: Conversion Coefficient B = 402
c14/402
Item 15: Conversion Coefficient C = 0 DEFAULT
Item 16: Retry Count = N/A N/A
DEFAULT = Default Data, it is not necessary to enter a command for this Item.
1 12V or higher is required for these sensors.
2 Gives result in mA for nominal 25.0Ω resistor. for maximum accuracy, use value of 1000/R where R is
the measured resistance of the current sense resistor from the resistor calibration data.
Notes: Item 9: Sensor warm-up time obtained from product manual.
PROCESSING MENU
ITEM DATA COMMAND ENTERED
Item 1: Process Category code = 1 (general) c1/1
Item 2: Process Type code = 1 (immediate) c2/1
Item 3: User-defined Process Name = 3 : Current c3/Current
Item 4: Sensor Input Channel = S1.13
current c3/S1.13
3 This value will vary depending on the number of sensors being connected to the ZENO®
-3200. To output
multiple values, repeat this menu as required. You can also refer directly to the sensor outputs,
rather than going through a process. In this case, enter S1.1 (for example to obtain the value
output by the 1st
defined sensor.
Notes: This process will simply display a current value from the sensors.
DATA OUTPUT MENU
ITEM DATA COMMAND ENTERED
Item 1: Field Type code = 9 : Transmit and Log Data Field c1/9
Item 2: Output Message(s) = 1 DEFAULT
Item 3: Field Name = cur c3/cur
Item 4: Data Process Record = P1.14
c4/P1.14
Item 5: Field Precision = 1 c5/1
Item 6: Field Width = 6 c6/6
Item 7: Data Storage Class Code = 8 : Compressed Float c7/8
DEFAULT = Default Data, it is not necessary to enter a command for this Item.
4 This value will vary depending on the number of sensors being connected to the ZENO®
-3200. To output
multiple values, repeat this menu as required. You can also refer directly to the sensor outputs,
rather than going through a process. In this case, enter S1.1 (for example to obtain the value
output by the 1st
defined sensor.
Note: If another process is setup, it is possible to record both a current value and
corresponding pH value for troubleshooting.

3. 3
Wiring Connections for 4 - 20 mA current loop interface:
1. 4 - wire sensor
2. 3 – Wire Sensor
Coastal
Environmental Systems (CES) supplies a precision, low temperature coefficient, 25.0Ω,
.1%, current sense resistor for 4 - 20 mA applications (CES P/N 1008Z). Sensor and
resistor leads should be twisted together and soldered or crimped together in a crimp
ferrule prior to connection into terminal block to provide a proper Kelvin connection.
After entering, make sure to save all of the setting by selecting (E) Save
Parameters To EEPROM.
Testing the Sensor
Since the pH and Conductivity are three-wire sensors, #2 is the appropriate way to wire
the probes. To see if value in real time, select the (T) Test Menu Option from the
User Menu. Select the option (Sx,y) Display Sensors x-y SCALED Data
To view the data as it is being read. If the value “10000” appears, give it a few cycles or
press “ESC” on the computer and try again until a reasonable number appears to be
displayed.
If everything is wired and functioning correctly, a value should appear that is the current
value. Another way to check whether the value is good is to wire the probe to a power

4. 4
supply and voltmeter as shown in the wiring diagrams of the probes manual and
determine whether the current values are in close proximity of each other for the buffer
that is tested.
It may be necessary to change the sampling time to perhaps 20 or 30 seconds under the
Sampling Period Menu located at the User Menu (the first one appearing when initially
logging into the Zeno 3200).
Calibrating the pH Probe (summary from the manual)
After is determined that the pH probe is returning a current reading, the next step is to
calibrate it. A pH buffer of 4 and a pH buffer of 10 will be required. Fill a container with
the pH 4 buffer and set the probe into the solution. Remember to remove the plastic
storage cap.
Let the sensor read the current value for 5 minutes and then record. Call it “W.”
For this example, it was found that W=8.1 mA when the probe is set into a pH 4 buffer.
Rinse the probe with DI water and place into a pH 10 buffer and leave for about 5
minutes. Record the value. For a pH of 10, the current reading was X=14.9 mA.
The rest of the arithmetic is as follows:
C = X – W = 14.9 – 8.1 = 6.8 (Step 7)
B = X – (C/6)(10) = 14.9 – (6.8/6)(10) = 3.6 (Step 8)
The value 3.6 is the low current value if the pH were 0.
The high current value is B + 14(6.3/6) = 19.5 (Step 10). If the pH were 14, 19.5 mA is
expected current value.
The final calculation is to convert the current value into pH value that can be recorded by
the datalogger.
In the case of linear sensor, to calculate B (A1) and C(A0), you need to know the
following values:
• The output current range of the sensor, vmin to vmax.
• The corresponding range in engineering units (pH or conductivity), xmin to xmax.
The slope B(A1) is given by the equation:
The offset C(A0) is given by the equation:

5. 5
After substituting the numbers, (14-0)/(19.5-3.6), B works out to 0.88. The value for C
works out to [(0*19.5)-(14)(3.6)]/15.9 = -3.17. Enter these values in to the process
record. Remember that the sensor needs to be checked at least once a month, so these
values could drift over time. After entering, make sure to save the parameters to
EEPROM or else if power loss occurs, the changes will be lost.
PROCESSING MENU
ITEM DATA COMMAND ENTERED
Item 1: Process Category code = 1 (general) c1/1
Item 2: Process Type code = 1 (immediate) c2/1
Item 3: User-defined Process Name = 3 : pH c3/pH
Item 4: Input for Data (X) = S1.13
current c3/S1.13
Item 5: A2 Coefficient 0 C5/0
Item 6: A1 Coefficient 0.88 C6/0.88
Item 7: A0 Coefficient -3.17 C7/-3.17
Calibrating the Conductivity Sensor
Fill a container with DI water and another with 5000 uS solution (or some concentration
significantly higher than zero). Record a current value for the DI water and another for
the higher concentration solution. Calculate like the pH but substitute appropriate values
for the conductivity solution and DI water.
References
1. Manual: Global Water Instrumentation, Inc.,11390 Amalgam Way,Gold
River, CA 95670,T: 800-876-1172,Int’l: (916) 638-3429, F: (916) 638-
3270,Temperature Sensor: WQ101, pH Sensor: WQ201,Conductivity
Sensor: WQ301, Dissolved Oxygen Sensor: WQ401, ORP/Redox: WQ600,
Web: http://www.globalw.com/
2. Manual: ZENO®-3200User Manual Version V2.02, June 27, 2003, P/N:
0302116012, Revision B, COASTAL ENVIRONMENTAL SYSTEMS, Inc.820
First Avenue South • Seattle, WA 98134 Telephone (206) 682-6048 • Fax (206)
682-5658, Web: http://www.coastalenvironmental.com/