Pyxis ST-774 User manual

ST-774 Dissolved Oxygen Sensor
User Manual
October 27, 2022
Rev. 1.2
Pyxis Lab, Inc.
1729 Majestic Dr. Suite 5
Lafayette, CO 80026 USA
www.pyxis-lab.com
© 2017 Pyxis Lab, Inc.
Pyxis Lab Proprietary and Confidential

Table of Contents
1Introduction ...................................................................................................................................2
1.1 Main Features...................................................................................................................................2
2Specifications..................................................................................................................................3
3Unpacking Instrument.....................................................................................................................4
3.1 Standard Accessories........................................................................................................................4
3.2 Optional Accessories & Services.......................................................................................................4
4Installation .....................................................................................................................................5
4.1 Piping................................................................................................................................................5
4.2 Wiring ...............................................................................................................................................6
4.3 Connecting via Bluetooth.................................................................................................................6
5Setup and Calibration with uPyxis® Mobile App...............................................................................7
5.1 Download uPyxis® Mobile App.........................................................................................................7
5.2 Connecting to uPyxis® Mobile App .................................................................................................. 7
5.3 Calibration Screen and Reading ....................................................................................................... 8
5.5 Device Info Screen..........................................................................................................................11
5.6 Diagnosis Screes……………………………………………………………………………………………………………………….. 11
6Setup and Calibration with uPyxis® Desktop App...........................................................................12
6.1 Install uPyxis® Desktop App............................................................................................................12
6.2 Connecting to uPyxis® Desktop App...............................................................................................12
6.3 Information Screen.........................................................................................................................13
6.4 Calibration Screen ..........................................................................................................................13
6.5 Diagnosis Screen.............................................................................................................................16
7Outputs........................................................................................................................................18
7.1 4–20mA Output Setup....................................................................................................................18
7.2 Adjusting 4–20mA Span .................................................................................................................18
7.3 Communication using Modbus RTU...............................................................................................19
8Sensor Maintenance and Precaution .............................................................................................20
8.1 Methods to Cleaning the ST-774 Sensor........................................................................................20
8.2 Storage............................................................................................................................................21
9Troubleshooting ...........................................................................................................................21
10 Contact Us ..................................................................................................................................21

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Warranty Information
Confidentiality
The information contained in this manual may be confidential and proprietary and is the property of Pyxis
Lab, Inc. Information disclosed herein shall not be used to manufacture, construct,or otherwise reproduce
the goods described. Information disclosed herein shall not be disclosed to others or made public in any
manner without the express written consent of Pyxis Lab, Inc.
Standard Limited Warranty
Pyxis Lab warrants its products for defects in materials and workmanship. Pyxis Lab will, at its option,
repair or replace instrument components that prove to be defective with new or remanufactured
components (i.e., equivalent to new). The warranty set forth is exclusive and no other warranty, whether
written or oral, is expressed or implied.
Warranty Term
The Pyxis warranty term is thirteen (13) months ex-works. In no event shall the standard limited warranty
coverage extend beyond thirteen (13) months from original shipment date.
Warranty Service
Damaged or dysfunctional instruments may be returned to Pyxis for repair or replacement. In some in-
stances, replacement instruments may be available for short duration loan or lease.
Pyxis warrants that any labor services provided shall conform to the reasonable standards of technical
competency and performance effective at the time of delivery. All service interventions are to be reviewed
and authorized as correct and complete at the completion of the service by a customer representative or
designate. Pyxis warrants these services for 30 days after the authorization and will correct any qualifying
deficiency in labor provided that the labor service deficiency is exactly related to the originating event. No
other remedy, other than the provision of labor services, may be applicable.
Repair components (parts and materials), but not consumables, provided during a repair, or purchased
individually, are warranted for 90 days ex-works for materials and workmanship. In no event will the in-
corporation of a warranted repair component into an instrument extend the whole instrument’s warranty
beyond its original term.
Warranty Shipping
A Repair Authorization (RA) Number must be obtained from Pyxis Technical Support before any product
can be returned to the factory. Pyxis will pay freight charges to ship replacement or repaired products to
the customer. The customer shall pay freight charges for returning products to Pyxis. Any product returned
to the factory without an RA number will be returned to the customer. To receive an RMA you can
generate a request on our website at https://pyxis-lab.com/request-tech-support/.
Pyxis Technical Support
Contact Pyxis Technical Support at [phone], [email protected]m, or by filling out a request for
support at https://pyxis-lab.com/request-tech-support/.

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1Introduction
The Pyxis ST-774 sensor is an ultra-low range dissolved oxygen (DO) sensor with a measurement range of
0.0 - 2,000 ppb and lower limit of detection 0.1 ppb (µg/L). It is based on the principle of fluorescence
quenching to determine the partial pressure of the dissolved oxygen in water. It incorporates Pyxis’
advanced technology in the field of fluorescence. The ST-774 offers the robustness associated with
optical/luminescent DO sensor technology while achieving the ultra-low detection limit compatible to an
amperometric DO sensor.
The ST-774 and other Pyxis dissolved oxygen sensors (ST-772 and ST-776) measure the oxygen partial pres-
sure that is at equilibrium with the dissolved oxygen in water. The relationship between the partial
pressure (PO2) and the concentration of the dissolved oxygen is governed by Henry’s law:
DO/ppb = KPO2. (1)
where K is Henry’s Law constant, which is a function of the temperature and the ionic strength (or conduc-
tivity) of the water sample. Pyxis uses the latest USGS equations to convert the measured partial pressure
and temperature measured by the built-in temperature sensor to a DO value in ppb (or µg/L) for the ST-
774 sensor.
The ST-774 sensor offers an easily replaceable, front loading DO membrane cap that has been indepen-
dently developed by Pyxis Lab, with a typical service life of up to two years. The flat front-end design of the
ST-774 sensor makes this platform less prone to contamination or fouling and is very easy to clean. The
sensor body is composed of 316L stainless steel and is well suited for aggressive industrial application use.
The ST-774 sensor offers both 4–20mA and RS-485 Modbus outputs and is Bluetooth enabled when used
in conjunction with the MA-CR or PowerPACK Series Bluetooth Adapters.
1.1 Main Features
The ST-774 sensor includes the following features:
•0.0–2,000 µg/L measurement range
•0.1 µg/L Lower Level of Detection
•Built-in temperature and pressure sensors
•Accurate and stable measurement with ultra-low drift
•Built-in transmitter without the need of using a preamplifier or meter head
•Dual outputs: isolated 4–20 mA signal and RS-485 Modbus
•Long-distance transmission with higher stability and accuracy
•Wireless calibration, diagnostics, data trend via uPyxis® App when used with MA-CR Adapter
•Zero-point calibration with nitrogen and slope calibration in O2-containing calibration gas
•Alternative Zero-Calibration using 5% Catalyzed Sodium Sulfite Solution
•ST-774 Service Program (P/N ST-774-SWAP)
(a) $700 Per Year Factory Calibrated/Reconditioned Sensor Only Exchange
(b) Client Issues PO#
(c) Pyxis sends a new or reconditioned unit
(d) Client sends Pyxis the unit in need of recalibration and service
(e) Even exchange –eliminates client calibration and maintenance

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2Specifications
Table 1. ST-774 Specifications
Item
Specification
P/N
53715
Output Range for DO
(4-20mA)
0.0 - 2,000 μg/L (ppb)
Temp Measuring Range (4-
20mA Output Scale)
Generation 2 only
32 –122oF (0 –50oC) +
0.2% of value
Lower Level of Detection
0.1 μg/L (ppb)
Dissolved Oxygen Resolution
0.1 μg/L (ppb)
Dissolved Oxygen Accuracy
± 0.3 μg/L (ppb) or ± 1%
Method
Blue Light Irradiated Excitation
Red Light Reference
Response Time (90%)
Liquid Phase <30s / Gas Phase <10s
Operational Temperature
0 °C –50 °C (32 - 122° F)
Operating Voltage
22 –26V DC, Power 0.6W
Signal Output
4-20mA analog output / RS-485 digital output
Dimension (L x D)
300 x 60mm (11.8 x 2.36 inches)
Weightᶧ
2150 g (4.74 lb.) cable excluded
Installation Method
¼ inch OD Swagelok
Suggested Flow Range
50 –500 mL/Minute
Sample Connection Format
Sample Line & Inlet Stainless Steel with Compression Fitting
Material of Construction
316L stainless steel
Working Pressure
Up to 145psi (10Bar)
Material of Construction
316L stainless steel
Cables Length
Attached 1.5 m/4.9 ft 8-Pin cable,
MA-1.5CR Cable (1.5 m/4.9 ft 8-Pin Male Adapter/Flying Lead)
Calibration
High Point Calibration：0.1% Oxygen in Nitrogen Gas
Zero Calibration: 5% Catalyzed Sodium Sulfite (12 hour soak)
-or-
99.999% Nitrogen Gas
DO Membrane Cap Life
2 years
Enclosure Rating
IP-67/IP-68
Regulation
CE / RoHS
* With Pyxis’s continuous improvement policy, these specifications are subject to change without
notice. †Cables excluded

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3Unpacking Instrument
Remove the instrument and accessories from the shipping container and inspect each item for any
damage that may have occurred during shipping. Verify that all accessory items are included. If any item
is missing or damaged, please contact Pyxis Lab Customer Service at [email protected].
3.1 Standard Accessories
The following accessories are included in the ST-774 sensor package (P/N 53715)
•One DCC-2 Dissolved Oxygen Membrane Cap
P/N: 53716
•One MA-1.5CR Cable (1.5 m/4.9 ft 8-Pin Male Adapter/Flying Lead)
P/N: 50746
•One MA-CR Bluetooth Adapter for 8-Pin Sensors
P/N: MA-CR
•One MA-NEB Bluetooth/USB Adapter for use with uPyxis® Desktop App
P/N: MA-NEB
•Sulfite Zero Calibration Cap
P/N 16019
• User Manual available online at ST-774 Ultra-Low Luminescent Dissolved Oxygen Sensor | Pyxis Lab®
(pyxis-lab.com)
3.2 Optional Accessories & Services
The following optional accessories can be ordered at [email protected]om or the Pyxis E-Store at
https://pyxis- lab.com/shop/
Table 2. Optional Accessories
Accessory Name
P/N
MA-CR Bluetooth Adapter For 8-Pin Pyxis Sensors
MA-CR
ST-774/776 Flow Cell Assembly —Replacement
53718
DCC-2 Dissolved Oxygen Membrane Cap —Replacement
53716
UC-50 Display & Data Logger
43007
Sulfite ZERO Calibration Kit (Includes Calibration Cap and 10mL Sulfite Powder)
16019
Replacement Catalyzed Sodium Sulfite Powder in 10mL vial
SO3-VIAL
MA-50CR Cable (15 m/50 ft 8-Pin Male/Female Extension Cable)
50743
MA-100CR (30.5 m/100 ft 8-Pin Male/Female Extension Cable)
50744
Pyxis Probe Cleaning Kit
SER-01
ST-774 SERVICE-SWAP PROGRAM —ANNUAL*
ST-774-SWAP
NOTE - PO# must be issued for ST-774 Service-Swap Program. Pyxis Ships New/Reconditioned ST-
774 Sensor Only. Client Ships Their Sensor to Pyxis for Even Exchange. 30-days to Ship Old Sensor or
Pyxis Bills for full value of New ST-774

ST-774 User Manual [e-mail] | [phone]
4Installation
4.1 Piping
The ST-774 sensor must always be installed in sample flow at or below the upper temperature limit of the
sensor (<122 °F).The sample line should always be stainless steel and utilize compression fitting adapters
at all junction points to avoid oxygen ingress into the sample water. Using plastic tubing for the sample
line and/or threaded-taped junctions will result in oxygen ingress and potential sensor inaccuracy or
extended periods of sensor stabilization.
The recommended sample flow rate to the ST-774 is 50 to 500mL/minute. Flows exceeding 500mL/ minute
may result in unstable oxygen readings. With proper installation using stainless steel sample lines and
thoroughly tightened compression fittings, the ST-774 should stabilize to a low level within a few hours
after startup. Once this has occurred, you may proceed with the oxygen study/evaluation. If stabilization
of the sensor takes a longer period of hours or days, please evaluate your installation for oxygen ingress
into the sample line and other on-site application parameters (i.e.. deaerator operating temperature,
pressure, feedwater flow rates, loss of oxygen scavenger feed etc.)
In many applications a sample pre-cooler will be required to adjust sample temperature to an acceptable
level. To properly install the ST-774 sensor, follow the steps below:
1. Mount the flow cell of the sensor to a flat surface.
2. Connect the flow cell’s 1/4” Swagelok ports are connected to the sample flow line and allow flow cell and
ports to fully drain.
3. Make sure that the O-ring is installed properly in the flow cell.
4. Hand-tighten the ST-774 sensor body to the flow cell.
Figure 2.
Pipeline installation using ST-774 Flow Cell Assembly
(P/N: 53718) with dimensions (mm)

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4.2 Wiring
Below are 2 wiring tables. The left represents the first generation of the ST-774 probe with only one 4-
20mA output for DO (produced before serial # 210026). The right represents the second generation of ST-
774 probe (produced after and including serial # 210026) containing two 4-20mA outputs, one for DO and
one for Temperature. Follow the wiring tables below to connect the ST-774 sensor to a controller based
on which sensor you have. *NOTE* The negative 24V power terminal (power ground) and the negative
4–20mA terminal on the ST-774 sensor are internally connected.
ST-774 First Generation ST-774 Second Generation
(Prior to Serial # 210026) (After and Including Serial # 210026
Color
Designation
Color
Designation
Red
24V+
Red
24V+
Brown
24V-
Brown
Power Ground
White
DO 4-20mA +
White
DO 4-20mA +
Grey
4-20mA –
Grey
4-20mA –
Pink
485GNDD
Pink
Temp 4-20mA+
Blue
RS-485 A
Blue
RS-485 A
Yellow
RS-485 B
Yellow
RS-485 B
Green
GNDD
Green
RS-485 C
NA
NA
Black
Shield
Measurement
4mA Value
20mA Value
Dissolved Oxygen
0 μg/L (ppb)
2,000 μg/L (ppb)
Temperature
(Generation 2 only See above)
32oF (0oC)
122oF (50oC)
Table 3
4.3 Connecting via Bluetooth
A Bluetooth adapter (P/N: MA-CR) can be used to connect a ST-774 sensor to a smart phone with the uPyxis®
Mobile App or a computer with a Bluetooth/USB Adapter (P/N: MA-NEB) and the uPyxis® Desktop App.
Figure 3. Bluetooth connection to ST-774 sensor MA-CR and uPyxis Mobile App.

ST-774 User Manual [e-mail] | [phone]
5Setup and Calibration with uPyxis® Mobile App
5.1 Download uPyxis® Mobile App
Download uPyxis® Mobile App from Apple App Store or Google Play.
Figure 4. uPyxis® Mobile App installation
5.2 Connecting to uPyxis® Mobile App
Connect the ST-774 sensor to a mobile smart phone according to the following steps:
1. Open uPyxis® Mobile App.
2. On uPyxis® Mobile App, pull down to refresh the list of available Pyxis devices.
3. If the connection is successful, the ST-774 and its Serial Number (SN) will be displayed (Figure 5).
4. Press on the ST-774 sensor image.
Figure 5.