Campbell CS526 User manual

CS526 ISFET pH Probe
Revision: 6/13
Copyright © 2009-2013
Campbell Scientific, Inc.

Warranty
The CS526 ISFET pH Probe is warranted for six (6) months subject to this
limited warranty:
“PRODUCTS MANUFACTURED BY CAMPBELL SCIENTIFIC, INC. are
warranted by Campbell Scientific, Inc. (“Campbell”) to be free from defects in
materials and workmanship under normal use and service for twelve (12)
months from date of shipment unless otherwise specified in the corresponding
Campbell pricelist or product manual. Products not manufactured, but that are
re-sold by Campbell, are warranted only to the limits extended by the original
manufacturer. Batteries, fine-wire thermocouples, desiccant, and other
consumables have no warranty. Campbell's obligation under this warranty is
limited to repairing or replacing (at Campbell's option) defective products,
which shall be the sole and exclusive remedy under this warranty. The
customer shall assume all costs of removing, reinstalling, and shipping
defective products to Campbell. Campbell will return such products by surface
carrier prepaid within the continental United States of America. To all other
locations, Campbell will return such products best way CIP (Port of Entry)
INCOTERM® 2010, prepaid. This warranty shall not apply to any products
which have been subjected to modification, misuse, neglect, improper service,
accidents of nature, or shipping damage. This warranty is in lieu of all other
warranties, expressed or implied. The warranty for installation services
performed by Campbell such as programming to customer specifications,
electrical connections to products manufactured by Campbell, and product
specific training, is part of Campbell’s product warranty. CAMPBELL
EXPRESSLY DISCLAIMS AND EXCLUDES ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A
PARTICULAR PURPOSE. Campbell is not liable for any special, indirect,
incidental, and/or consequential damages.”

Assistance
Products may not be returned without prior authorization. The following
contact information is for US and international customers residing in countries
served by Campbell Scientific, Inc. directly. Affiliate companies handle
repairs for customers within their territories. Please visit
www.campbellsci.com to determine which Campbell Scientific company serves
your country.
To obtain a Returned Materials Authorization (RMA), contact CAMPBELL
SCIENTIFIC, INC., phone [phone]. After an applications engineer
determines the nature of the problem, an RMA number will be issued. Please
write this number clearly on the outside of the shipping container. Campbell
Scientific's shipping address is:
CAMPBELL SCIENTIFIC, INC.
RMA#_____
815 West 1800 North
Logan, Utah 84321-1784
For all returns, the customer must fill out a "Statement of Product Cleanliness
and Decontamination" form and comply with the requirements specified in it.
The form is available from our web site at www.campbellsci.com/repair. A
completed form must be either emailed to [e-mail] or faxed to
[phone]. Campbell Scientific is unable to process any returns until we
receive this form. If the form is not received within three days of product
receipt or is incomplete, the product will be returned to the customer at the
customer's expense. Campbell Scientific reserves the right to refuse service on
products that were exposed to contaminants that may cause health or safety
concerns for our employees.

Table of Contents
PDF viewers: These page numbers refer to the printed version of this document. Use the
PDF reader bookmarks tab for links to specific sections.
1. Introduction.................................................................1
2. Cautionary Statements...............................................1
3. Initial Inspection .........................................................2
4. Quickstart ....................................................................2
5. Overview......................................................................3
6. Specifications .............................................................3
7. Installation and Wiring ...............................................4
7.1 Preparation for Use ..............................................................................4
7.2 Wiring ..................................................................................................4
8. Programming ..............................................................5
8.1 Get Data Command..............................................................................5
8.2 CRBasic Programming.........................................................................5
8.2.1 Instruction Sequence.....................................................................5
8.2.2 Instruction Descriptions ................................................................6
8.2.2.1 SerialOpen() Instruction.....................................................6
8.2.2.2 SerialOut() Instruction........................................................6
8.2.2.3 SerialIn() Instruction ..........................................................6
8.2.2.4 SplitStr() Instruction...........................................................7
8.2.3 Example Program..........................................................................7
8.2.4 Programming for Calibration ........................................................7
9. Calibration ...................................................................8
10. Troubleshooting..........................................................8
11. Maintenance ................................................................9
11.1 Cleaning ...............................................................................................9
11.1.1 When to Clean...............................................................................9
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Table of Contents
ii
11.1.2 Cleaning Procedure .................................................................... 10
11.1.2.1 Cleaning Tips................................................................... 10
11.1.3 Revitalizing ................................................................................ 11
11.2 Storage............................................................................................... 11
11.2.1 Short-Term Storage (2 days or less)........................................... 11
11.2.2 Long-Term Storage (more than 2 days) ..................................... 11
Appendix
A. Calibration ...............................................................A-1
A.1 Example Calibration Program ......................................................... A-2
Figures
11-1. Tip of the CS526 probe ..................................................................... 10
Tables
7-1. CR800, CR850, CR1000, and CR3000 Wiring................................... 4
8-1. “Get Data” Command and Response................................................... 5
8-2. Instruction Sequence ........................................................................... 5
9-1. Calibration Standards .......................................................................... 8

CS526 ISFET pH Probe
1. Introduction
The CS526 ISFET pH Probe measures pH from 1 to 14 in aqueous or semi-
solid solutions. It outputs TTL serial data that is read by compatible
dataloggers (see Section 6, Specifications).
Before using the CS526, please study
•Section 2, Cautionary Statements
•Section 3, Initial Inspection
•Section 4, Quickstart
More detailed instructions for operation, troubleshooting, and maintenance are
available in the remaining sections.
2. Cautionary Statements
•Campbell Scientific warranty does not cover a clogged reference diaphragm or
improperly cleaned or maintained ISFET chip (see Section 11, Maintenance).
•Maximum input voltage is 5 Vdc. Incorrect wiring may cause performance
loss and irreversible damage.
•To prevent scratching the sensor chip when cleaning, first soak the sensor in
soapy water and then gently scrub with a toothbrush (see Section 11,
Maintenance). Most scratches occur when hard particles are rubbed on the
chip surface. Scratches cause irreversible damage to the probe.
•Do not use hydrofluoric acid, acetone, MEK, or similar agents to clean the
probe.
•Cable can be damaged by abrasion, rodents, sharp objects, twisting, crimping
or crushing, and pulling. Take care during installation and use to avoid cable
damage.
•The CS526 is rugged, but it should be handled as a precision scientific
instrument.
•The CS526 has no user-serviceable parts. Any attempt to disassemble the
device will void the six-month warranty.
•Care should be taken when opening the shipping package to not damage or cut
the cable jacket. If damage to the cable is suspected, consult with a Campbell
Scientific applications engineer.
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CS526 ISFET pH Probe
3. Initial Inspection
Upon receipt of the CS526, inspect the packaging and contents for damage.
File damage claims with the shipping company.
The model number and cable length are printed on a label at the connection end
of the cable. Check this information against the shipping documents to ensure
the correct product and cable length are received.
4. Quickstart
For complete installation, programming, and calibration information, see
Sections 7through 9.
The CS526 is shipped dry. Before the probe can be calibrated, it must be
soaked in 7-pH buffer solution for 15 minutes. Follow the calibration
procedure outlined in Appendix A, Calibration.
Unlike many glass-bulb type pH sensors, the CS526 ISFET pH probe can be
installed without regard to orientation. Connect the CS526 to the datalogger
according to the following table. Be sure to connect Red to the 5V channel.
Wire Color Datalogger Connection
Red (Caution! 5 Vdc max!) 5V
Black G
White Control Port (Tx)
Green Control Port (Rx)
Clear G
Program the datalogger as follows.
'CR1000 Series Datalogger
'Declare variable for digital pH measurement
Public pHCount
'Declare variables for serial input from sensor
Dim rawstring As String * 20, pHDigit(2)
'Main Program
BeginProg
'Set up datalogger port for serial communication
SerialOpen ( Com1,2400,16,0,41)
'Establish program scan rate of 60 seconds
Scan (60,Sec,0,0)
'Send get data command to CS526
SerialOut (Com1,"1M1!"&CHR(13),"",0,0)
'Set up COM1 to receive incoming serial data.
'Set timeout to maximum 200 mS
SerialIn (rawstring,Com1,20,0,20)
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CS526 ISFET pH Probe
'Split out digital count value for pH from string input
SplitStr (pHDigit(),rawstring,"String",2,0)
pHCount = pHDigit(2)
NextScan
EndProg
5. Overview
The submersible CS526 is designed to reliably provide accurate pH
measurements over the specified operating temperature range. The pH-
sensitive element is SENTRON’s Ion Sensitive Field Effect Transistor (ISFET)
semi-conductor, which includes a silver / silver chloride – potassium chloride
reference system. This technology is one of the most significant breakthroughs
in pH testing in half a century and is considered one of the most robust pH
testing technologies available today.
The CS526 is suitable for demanding applications in laboratory and field. The
ISFET performs well in solutions with high solids, moderately aggressive
chemicals, and biological materials. Clogging and junction-contaminating
conditions are well tolerated. See Section 11, Maintenance, for cleaning
procedures.
CS526 electronics are embedded in durable PEEK material, which makes up
the sensor body. The absence of a glass electrode eliminates the potential
hazard of broken glass. The ISFET design considerably reduces the number of
acidic or alkaline errors in extreme pH conditions.
6. Specifications
Features:
•Safety —the ISFET with durable PEEK material can be used safely
in applications where broken glass is a hazard to the user.
•Intelligent electronics —the CS526 combines the latest
developments in ISFET pH sensing technology with state-of-the-art
signal processing. This allows for accurate, fast and reliable results.
•Quality —designed and manufactured under stringent quality control
conditions in an ISO 9001 environment. Each sensor is individually
tested to the most demanding testing protocols, and the electronics
comply fully with directives and with EMC standard
IEC61326:2005.
Compatibility: CR800-series, CR1000, CR3000 dataloggers
Measurement
Range: 1 to 14 pH
Accuracy: ±0.2 pH with 2-point calibration
24 hr drift: <0.15 pH (after 15-min soak in pH 7 at 25°C)
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CS526 ISFET pH Probe
Operating
Temperature: 10° to 40°C
Water Pressure: 0 to 700 kPa (0 to 101.5 psi)
Power Requirement
Source: 5 Vdc
Load: 15 mA maximum
Output: TTL logic, 2400 bps
8 data bits, no parity, 1 stop bit
Maximum Cable Length: 100 m (328 ft)
Cable Type: Three-twisted pair, 24-AWG cable with
Santoprene®jacket
Sensor Material: PEEK
Weight
w/10-ft cable: 318 g (11.2 oz)
Dimensions
Length: 102 mm (4 in)
Diameter: 16 mm (0.63 in)
Certifications: ISO 9001
compliant
EMC standard IEC61326:2005
7. Installation and Wiring
7.1 Preparation for Use
The CS526 is shipped dry. Before the probe can be calibrated, soak it in 7-pH
buffer solution for 15 minutes. Unlike many glass-bulb type pH sensors, the
CS526 ISFET pH probe can be installed without regard to orientation.
7.2 Wiring
TABLE 7-1. CR800, CR850, CR1000, and CR3000 Wiring
Wire Color Wire Label/Function Datalogger Connections
Red (see following
caution)
Power 5V 5V
Black Ground G
White Signal #1 (Rx) Control Port (Tx)
Green Signal #2 (Tx) Control Port (Rx)
Clear Shield G
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CS526 ISFET pH Probe
This probe must be connected to the datalogger’s 5V
terminal (not 12V). Connecting to a higher voltage will
damage the probe beyond repair.
CAUTION
8. Programming
8.1 Get Data Command
The datalogger needs to send a “get data” serial command to the CS526 to get
the pH data. This command is sent to the CS526 via the SerialOut() CRBasic
instruction (see Section 8.2.2.2, SerialOut() Instruction). TABLE 8-1 shows
the “get data” command and its response.
TABLE 8-1. “Get Data” Command and Response
Command Response
aMn!<CR>
Where:
a = probe address (factory
default is 1)
n = a single dummy character
(typically use 1)
a<value><CR><LF>
Where:
a = probe address (factory default is 1)
<value> = the probe’s reading for pH (in
digital counts).
8.2 CRBasic Programming
8.2.1 Instruction Sequence
A sequence of CRBasic instructions is used to measure the sensor. TABLE 8-2
shows the instruction sequence. Information about the instructions is provided
in Section 8.2.2, Instruction Descriptions, and an example program is provided
in Section 8.2.3, Example Program.
TABLE 8-2. Instruction Sequence
Instruction Function
SerialOpen() Set up a datalogger port for serial communication (see Section
8.2.2.1, SerialOpen() Instruction)
Scan() Establish a scan rate
SerialOut() Send “get data” command to the CS526.
See Section 8.1, Get Data Command, and 8.2.2.2, SerialOut()
Instruction, for more information.
SerialIn() Set up the COM port to receive the incoming serial data (see
Section 8.2.2.3, SerialIn() Instruction).
Please note that in the beginning of the CRBasic program, the
variable used in the SerialIn() instruction needs to be
declared as an ASCII string format.
SplitStr() Split out digital count value for pH from the input string.
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CS526 ISFET pH Probe
Probe output is “Counts”. A corrected multiplier and offset are
required to provide an output in pH units (see Appendix A,
Calibration).
NOTE
8.2.2 Instruction Descriptions
8.2.2.1 SerialOpen() Instruction
The SerialOpen() instruction has the following syntax:
SerialOpen(ComPort,BaudRate,Format,TXDelay,BufferSize)
ComPort —the datalogger COM port in which the probe is connected.
BaudRate —choose 2400
Format —choose 16, which is TTL Logic; No parity, one stop bit, 8 data
bits; No error checking
TXDelay —enter 0
BufferSize —enter at least twice the number of maximum expected
characters + 1, which is 41.
8.2.2.2 SerialOut() Instruction
The SerialOut() instruction has the following syntax:
SerialOut(ComPort,OutString,WaitString,NumberTries,TimeOut)
ComPort —the datalogger COM port in which the probe is connected.
OutString —use "1M1!"+CHR(13) for the OutString when the default
probe address of 1 is used.
WaitString —enter the null (“”) WaitString to tell the datalogger to wait
for the echo of each character in the OutString
NumberTries —enter 0
TimeOut —specifies the time, in 0.01 seconds, that the datalogger should
wait for the WaitString or echo of each character in the OutString (0
is used in the example program).
8.2.2.3 SerialIn() Instruction
The SerialIn() instruction has the following syntax:
SerialIn(Dest,ComPort,TimeOut,TerminationChar,MaxNumChars)
Dest —specifies the variable in which the incoming data will be stored.
Please note that in the beginning of the CRBasic program, this
variable needs to be declared as ASCII string format (see example
program in Section 8.2.3, Example Program)
ComPort —the datalogger COM port in which the probe is connected.
TimeOut —20 should be adequate, which gives a 200 ms maximum delay
time. The TimeOut parameter is used to specify the amount of time,
in 0.01 seconds, that the datalogger should wait before proceeding to
the next instruction.
TerminationChar —enter 0
MaxNumChars —20 should be adequate (specify the maximum number
of characters to expect per input)
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CS526 ISFET pH Probe
8.2.2.4 SplitStr() Instruction
The SplitStr() instruction has the following syntax:
SplitStr(SplitResult,SearchString,FilterString,NumSplit,SplitOption)
SplitResult —an array in which the split string will be stored.
SearchString —the string on which this instruction will operate. This will
be the variable entered for the Dest parameter for the SerialIn()
instruction (see above).
FilterString —enter “String” (this value will be ignored because of the
SplitOption that will be used).
NumSplit —enter 2
SplitOption —enter 0. This splits out numeric values.
8.2.3 Example Program
The following is a CR1000 program that measures the CS526. This program
assumes the CS526 is connected to COM1 (C1 / TX and C2 / RX) on the
CR1000.
'CR1000 Series Datalogger
'Declare variable for digital pH measurement
Public pHCount
'Declare variables for serial input from sensor
Dim rawstring As String * 20, pHDigit(2)
'Main Program
BeginProg
'Set up datalogger port for serial communication
SerialOpen ( Com1,2400,16,0,41)
'Establish program scan rate of 60 seconds
Scan (60,Sec,0,0)
'Send get data command to CS526
SerialOut (Com1,"1M1!"&CHR(13),"",0,0)
'Set up COM1 to receive incoming serial data.
'Set timeout to maximum 200 mS
SerialIn (rawstring,Com1,20,0,20)
'Split out digital count value for pH from string input
SplitStr (pHDigit(),rawstring,"String",2,0)
pHCount = pHDigit(2)
NextScan
EndProg
8.2.4 Programming for Calibration
To output in pH units instead of digital counts, enter the offset and multiplier
into the datalogger program. Simple program instructions can be used to make
the required periodic calibration easier. See Appendix A, Calibration, for an
example program.
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CS526 ISFET pH Probe
9. Calibration
Calibration should be carried out according to the detailed procedure outlined
in Appendix A, Calibration. The calibration should utilize two or more pH
standards, listed in TABLE 9-1, which are available from Campbell Scientific.
TABLE 9-1. Calibration Standards
pH Part Number
4 25587
7 25586
10 25588
Frequency of calibration depends on the level of accuracy required and the
coating / fouling nature of the measured samples.
10. Troubleshooting
If the CS526 is not operating properly and requires return to
Campbell Scientific, first obtain an RMA (returned material
authorization) and fill out the Declaration of Hazardous Material
and Decontamination form. This information is available at
www.campbellsci.com/repair.
NOTE
The most common causes for erroneous pH data include:
•poor sensor connections to the datalogger
•damaged cables
•scratched chip
•contaminated or clogged diaphragm
Problem:
Output signal is at its maximum value.
Possible reasons:
oProbe is not in fluid.
oChip is polluted.
oDiaphragm is polluted.
oChip is scratched.
Suggestions:
oPut probe in fluid.
oClean probe (Section 11.1, Cleaning).
oProbe cannot be fixed if chip is scratched.
Problem:
Probe response is very slow.
Possible reason:
oDiaphragm is chipped or polluted.
Suggestion:
oClean probe (Section 11.1, Cleaning).
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CS526 ISFET pH Probe
Problem:
Probe signal is drifting.
Possible reasons:
oDiaphragm can be dried out.
oChip is scratched.
Suggestions:
oSoak probe for 10 minutes in saturated KCl solution (pn 16349).
oProbe cannot be fixed if chip is scratched.
11. Maintenance
The CS526 needs to be periodically cleaned and calibrated
to ensure accurate readings and proper operation.
CAUTION
The CS526 has no user-serviceable parts.
11.1 Cleaning
Proper maintenance of a probe is important. If the probe is not properly and
regularly cleaned, the probe can malfunction due to a contaminated diaphragm
or ISFET chip. Contamination on/or blockage of the sensor and reference
electrode diaphragm surface is the most likely cause for probe failure.
Probe wear is another cause for probe failure. Probe wear is often, but not
necessarily, preceded by a period of declining calibration slope values. Probe
wear is dependent on how the probe is used and stored (see Section 11.2,
Storage). Worn probes need to be replaced.
11.1.1 When to Clean
Often the probe should be cleaned daily, but the appropriate cleaning frequency
is dependent on the type of sample being measured.
Clean the probe if any of the following occur:
•Low slope
•Drift
•Instability of the reading
•Slow calibration
•Probe will not calibrate
•pH value doesn’t change as expected when changing samples
Additionally, when sampling colored liquids, the probe should be cleaned
when the reference diaphragm is no longer white.
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CS526 ISFET pH Probe
11.1.2 Cleaning Procedure1.1.2 Cleaning Procedure
Read Section 11.1.2.1, Cleaning Tips, before following this procedure.Read Section 11.1.2.1, Cleaning Tips, before following this procedure.
1. Place probe in warm tap water (~60°) with a mild detergent and soak for 5
minutes, stir periodically.
1. Place probe in warm tap water (~60°) with a mild detergent and soak for 5
minutes, stir periodically.
2. Scrub the surface of the chip and the diaphragm (FIGURE 11-1) with a
soft toothbrush and water with a mild detergent (see Caution).
2. Scrub the surface of the chip and the diaphragm (FIGURE 11-1) with a
soft toothbrush and water with a mild detergent (see Caution).
Never brush the probe tip, especially the ISFET chip,Never brush the probe tip, especially the ISFET chip,
CAUTION
before rinsing and flushing thoroughly with water. Before
rinsing debris and particles may be on the sensor surface
and brushing them into the sensor may damage it. When
in doubt, soak the probe for a while in warm water with a
mild detergent.
Diaphragm
Chip
FIGURE 11-1. Tip of the CS526 probe
3. Rinse thoroughly with deionized water.
4. Revitalize the probe (Section 11.1.3, Revitalizing)
5. Calibrate the probe (Appendix A, Calibration).
11.1.2.1 Cleaning Tips
•To avoid scratches on the sensor surface, rinse the probe thoroughly using
water before cleaning the probe with the soft brush supplied with the meter
and tap water with a mild detergent added. Most scratches on the sensor
are caused when there are hard particles in the sample and the sample is
rubbed into the sensor when cleaning with the toothbrush.
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CS526 ISFET pH Probe
•Proteins, fats, and oils may be removed by scrubbing in a solution of Terg-
A-Zyme (Alconox company), a pepsin solution, or a similar product.
Afterwards, rinse thoroughly with deionized or distilled water.
•Do not use hydrofluoric acid, acetone, MEK, or similar agents to clean the
probe.
11.1.3 Revitalizing
Revitalization is performed to regenerate the diaphragm in the pH probe. For
best results, clean the probe first as described in Section 11.1.2, Cleaning
Procedure, before revitalizing.
1. Make sure the probe is warm (around 60°C).
2. Place the probe directly (without flushing it with deionized water or
cooling it down) in a saturated KCl-solution (pn 16349) at room
temperature and keep it in the solution for 20 minutes.
This cold KCl-dip will regenerate the reference system and the diaphragm.
11.2 Storage
11.2.1 Short-Term Storage (2 days or less)
1. Clean the probe first with water and possibly a mild detergent.
2. Place it in a clean container with fresh pH7 buffer solution (pn 25586) to
prevent contamination of the probe directly after cleaning.
11.2.2 Long-Term Storage (more than 2 days)
1. Clean the probe first with water and possibly a mild detergent.
2. Place one drop of demi-water in the probe’s protective cap.
3. Place the protective cap on the probe tip.
Always revitalize and recalibrate the probe before using it
again after long term storage (see Section 11.1.3,
Revitalizing, and Appendix A, Calibration).
CAUTION
11

CS526 ISFET pH Probe
12

Appendix A. Calibration
This calibration process uses 7-pH and 4-pH buffer solutions.
Protect the sensing chip from UV radiation during calibration. If
calibrating in sun or fluorescent light, shield the sensing chip
from UV radiation by using dark containers for the buffer
solutions.
NOTE
Load the example CRBasic program into the datalogger (Appendix A.1,
Example Calibration Program). Wire the CS526 to the datalogger according
to the following diagram.
Wire Color Datalogger Connection
Red (Caution! 5 Vdc Max!) 5V
Black G
White Control Port (Tx)
Green Control Port (Rx)
Clear G
Use the Numeric Display found in the datalogger software PC200W, PC400,
LoggerNet, PConnect, or PConnectCE to monitor the measurement in real
time.
1. Place the CS526 into a pH-7 buffer solution (pn 25586).
2. Monitor the [pHmV] reading in the Numeric Display and allow it to
stabilize.
3. Change the value in [pH7record] to -1.
4. Remove the CS526 from the pH-7 buffer solution and rinse with deionized
water.
5. Blot the CS526 dry with a soft cloth or paper towel.
6. Place the CS526 in a pH-4 buffer solution (pn 25587).
7. Allow the [pHmV] reading to stabilize.
8. Change the value in [pH4record] to -1.
9. Change the value in [pHcal] to -1.
10. The CS526 is now ready to be placed in the solution to be measured.
A-1

Appendix A. Calibration
A-2
A.1 Example Calibration Program
Following is a simple example program to facilitate the two-point calibration.
Although this is a CR1000 program, the other dataloggers are programmed
similarly.
'CR1000 Series Datalogger
'Define Variables
Public pH, pHCount
Public PTemp, batt_volt
Public pH4record, pH4Count
Public pH7record, pH7Count
Public pHcal, pHmult1
Public pHoffset1
Dim rawstring As String * 20, pHDigit(2)
'Define Data Tables
DataTable (TenMin,1,-1)
DataInterval (0,10,Min,10)
Average (1,pH,FP2,False)
EndTable
'Main Program
BeginProg
SerialOpen (Com1,2400,16,0,41)
Scan (10,Sec,0,0)
PanelTemp (PTemp,250)
Battery (batt_volt)
SerialOut (Com1,"1M1!"&CHR(13),"",0,0)
SerialIn (rawstring,Com1,20,0,20)
SplitStr (pHDigit(),rawstring,"String",2,0)
pHCount = pHDigit(2)
'Calibration
If PH4record = -1 Then
pH4Count = pHCount
pH4record = 0
EndIf
If pH7record = -1 Then
pH7Count = pHCount
pH7record = 0
EndIf
If pHcal = -1 Then
pHmult1 = 3/(pH7Count - pH4Count)
pHoffset1 = 7 - pHmult1 * pH7Count
pHcal = 0
EndIf
pH = pHmult1 * pHCount + pHoffset1
CallTable TenMin
NextScan
EndProg