RS-485 pH Probe AT-SB-PROBE-pH-P

Datasheet

1. Introduction

SENSBLUE pH POM AT-SB-PROBE-pH-P sensor is used in environmental water quality monitoring, acid/alkali/salt solutions, chemical reaction processes, and industrial production processes. It can meet the requirements of online pH measurement for most industrial applications.

2. Features

Signal output: RS-485 (Modbus/RTU protocol).
Convenient connection to third-party equipment such as PLCs, DCS, industrial control computers, general controllers, paperless recorders, or touch screens.
Double high-impedance differential amplifier with strong anti-interference capability and fast response.
The pH probe’s internal reference solution oozes very slowly from the microporous salt bridge under a pressure of at least 100 kPa (1 bar), and its forward bleed continues for more than 20 months. Such a reference system is very stable, and the electrode life is extended by a factor of two compared to conventional industrial electrodes.
Easy to install: 3/4 NPT pipe thread for easy submersible installation or installation in pipes and tanks.

3. Technical Specifications

Model	pH POM AT-SB-PROBE-pH-P
Measuring Range	0～14pH
Accuracy	±0.1pH
Resolution	0.01pH
Temperature Range	0 ~65℃
Work Pressure	＜0.2MPa
Temperature Compensation	automatic temperature compensation
Output	RS-485, MODBUS protocol
Power Supply	12～24VDC ±10%
Wetted Part Material	POM
Installation	Immersion mounting, 3/4 NPT thread
Cable Length	5 m, customizable
Calibration Method	Two-point calibration
Power Consumption	＜0.3W@12V
Ip Grade	IP68

4. Dimensions

The sensor connector is M16-5 core waterproof male connector.

5. Installation and Electrical Connection

5.1 Install

Note: The sensor must not be installed horizontally or upside down. It should be mounted at an inclination of at least 15° to ensure correct operation.

Pinouts
1 - Pin 12-24V DC	4 - RS485 B-
2 - GND	5 – NA
3 - RS485 A+	6 - NA
7 - NA

6. Maintenance

6.1 Use and maintenance

When measuring with the pH sensor, it should be cleaned in distilled water (or deionized water), and filter paper should be used to absorb the moisture to prevent impurities from being introduced into the solution to be tested. One-third of the sensor should be inserted into the solution being measured. When not in use, the sensor should be washed and placed in a protective sleeve containing a 3.5 mol/L potassium chloride solution or inserted into a container with the same 3.5 mol/L potassium chloride solution. Check whether the terminal is dry. If it is stained, wipe it with absolute alcohol and allow it to dry. Avoid long-term immersion in distilled water or protein solutions and prevent contact with silicone grease. Over time, the sensor’s glass membrane may become translucent or accumulate deposits, it can be cleaned with dilute hydrochloric acid and then rinsed with water. If the sensor is used for a long period and measurement errors occur, it must be calibrated using the meter. If calibration and measurement cannot be performed even after maintaining the sensor as described above, the sensor has failed. Please replace the sensor.

Standard Buffer Ph Reference Table

Temp(°C )	4.00	4.01	6.86	7.00	9.18	10.01
0	4.00	4.00	6.98	7.12	9.46	10.32
5	4.00	4.00	6.95	7.09	9.39	10.25
10	4.00	4.00	6.92	7.06	9.33	10.18
15	4.00	4.00	6.90	7.04	9.28	10.12
20	4.00	4.00	6.88	7.02	9.23	10.06
25	4.00	4.01	6.86	7.00	9.18	10.01
30	4.01	4.02	6.85	6.99	9.14	9.97
35	4.02	4.02	6.84	6.98	9.17	9.93
40	4.03	4.04	6.84	6.97	9.07	9.89
45	4.04	4.05	6.83	6.97	9.04	9.86
50	4.06	4.06	6.83	6.97	9.02	9.83

The actual reading and standard of the instrument sometimes have an error of ±1 digit.

6.2 Calibration

Note: the sensor has been calibrated at the factory, if not exceeding the measurement error, the calibration should not be random.

a.) Zero calibration

Use 250 mL of distilled water in a measuring cylinder, pour it into a beaker, add a packet of calibration powder with pH = 6.86, and stir evenly with a glass rod until the powder is completely dissolved. Prepare the solution with a pH of 6.86, place the sensor into the solution, and wait for 3–5 minutes. After the value stabilizes, check whether the displayed value is 6.86. If not, zero calibration is required. Refer to the appendix for calibration instructions.

b) Slope calibration

“For acidic solution: Take 250 mL of distilled water in a measuring cylinder, pour it into a beaker, add a packet of calibration powder with pH = 4.00, and stir evenly with a glass rod until the powder is completely dissolved. Prepare the solution to pH = 4.00. Place the sensor into the solution and wait for 3 to 5 minutes. After the value stabilizes, check whether the value is 4.00. If not, slope calibration is required. Refer to the appendix for the calibration instructions.

For alkaline solution: Take 250 mL of distilled water in a measuring cylinder, pour it into a beaker, add a packet of calibration powder with pH = 9.18, and stir evenly with a glass rod until the powder is completely dissolved. Prepare the solution to pH = 9.18. Place the sensor into the solution and wait for 3 to 5 minutes. After the value stabilizes, check whether the display shows 9.18. If not, slope calibration is required. Refer to the appendix for the calibration instructions.

7. Appendix data communication

7.1 Data Format

The default data format for Modbus communication is: 9600, n, 8, 1 (baud rate 9600 bps, 1 start bit, 8 data bits, no parity, 1 stop bit).

Parameters such as the baud rate can be customized.

7.2 Information Frame Format

a) Read data instruction frame

06 03 xx xx xx xx xx xx

Address Function code Register address Number of registers CRC check code (low byte first)

b) Read data response frame

06 03 xx xx xx xx xx xx

Address Function code Bytes Answer data RC check code (low byte first)

c) Wriite data instruction frame

06 06 xx xx xx xx xx xx

Address Function code Register address Wriite data CRC check code (low byte first)

d) Write data response frame (same data command frame)

06 06 xx xx xx xx xx xx

Address Function code Register ddress Write data CRC check code (low byte first)

7.3 Register Address

Register Address	Name	Description	Number Of Registers	Interview Method
40001(0x0000)	Measured pH + temperature	4 double-byte integers, which are the measured pH, the measured pH number of decimal places, the temperature value, and the decimal value of the temperature value.	4 ( 8 bytes)	Read
44097(0x1000)	Zero calibration	Calibrated in a standard solution with a pH of 6.86, writing data to 0	1 ( 2 bytes)	Write
44099(0x1002)	Slope calibration (4pH)	Calibrated in a standard solution with a pH of 4.00, writing data to 0	1 ( 2 bytes)	Write
44101(0x1004)	Slope calibration (9.18pH)	Calibrated in a standard solution with a pH of 9.18, writing data to	1 ( 2 bytes)	Write
44103(0x1006)	Zero calibration value	The data is read out as a zero offset.	1 ( 2 bytes)	Read
44105(0x1008)	Slope calibration value	The read data is the slope value x1000	1 ( 2 bytes)	Read
44113(0x1010)	Temperature calibration	Calibrated in solution, the data written is the actual temperature value x10 ; the read data is the temperature calibration offset x10 .	1 ( 2 bytes)	Write/Read
48195(0x2002)	Sensor address	The default is 6 and the data range is 1-127	1 ( 2 bytes)	Write/Read
48225(0x2020)	Reset sensor	The calibration value is restored to the default value and the write data is 0. Note: the sensor needs to be calibrated again after resetting.	1 ( 2 bytes)	Write

Note: Modbus register address according to the protocol defined with the register type register start address (16 hex represents the actual starting address register in parentheses).

a) When changing the sensor address, the sensor address in the return command is the changed new address.

b) The data definition that returns the measured value when reading data:

xx xx xx xx xx xx xx xx

2- byte measurement 2-byte measurement / Scale value scale number 2-byte temperature value 2-byte temperature

The data type defaults to: double-byte integer, high byte first; others are optional as floating-point types.

7.4 Command example

a.) Read data instruction

Function: Obtain the pH and temperature of the measuring probe; the unit of pH is pH; the unit of temperature is °C.

Request frame: 06 03 00 00 00 04 45 BE;

Response frame: 06 03 08 00 62 00 02 01 01 00 01 24 59

Example of reading:

pH value	Temperature value
00 62 00 02	01 01 00 01

pH: 00 62 indicates the hexadecimal reading pH value, 00 02 indicates that the pH value has 2 decimal places and is converted to a decimal value of 0.98.

Temperature value: 01 01 indicates the hexadecimal reading temperature value, 00 01 indicates that the temperature value has 1 decimal place and is converted to a decimal value of 25.7.

b.) Calibration instructions:

Zero calibration

Function: Set the pH zero calibration value of the electrode. The zero value is based on the 6.86 pH standard. The examples are as follows;

Request frame: 06 06 10 00 00 00 8C BD

Response frame: 06 06 10 00 00 00 8C BD

Slope calibration

Function: Set the pH slope calibration value of the electrode. The slope calibration is divided into high‑point and low‑point calibration. The alkaline solution is measured at the high point, and the acidic solution is measured at the low point. The standard solutions used are 9.18 pH for the high point and 4.00 pH for the low point. Examples are as follows:

High point standard solution 9.18 pH calibration:

Request frame: 06 06 10 04 00 00 CD 7C

Response frame: 06 06 10 04 00 00 CD 7C Low

standard solution 4.00 pH calibration:

Request frame: 06 06 10 02 00 00 2D 7D

Response frame: 06 06 10 02 00 00 2D 7D

c) Set the device ID address:

Role: set the MODBUS device address of the electrode;

Change the device address 06 to 01.

The example is as follows

Request frame: 06 06 20 02 00 01 E3 BD

Response frame: 06 06 20 02 00 01 E3 BD

7.5 Error response

If the sensor does not execute the host command correctly, it will return the following format information:

Definition	Address	Function Code	CODE	CRC check
data	ADDR	COM+80H	Xx	CRC 16
Number of bytes	1	1	1	2

d) CODE : 01 – function code error

03 – data is wrong

e) COM : Received function code

8. Applicable Accessories

	Name	Requirements
PA000000076	SENSBLUE MONARCH Solar Panel 1 Probe
PA000000079	SENSBLUE MONARCH Solar Panel 2 Probes
PA000000080	SENSBLUE MONARCH Solar Panel 1 Probe External Antenna
PA000000074	SENSBLUE MONARCH Solar Panel 2 Probes External Antenna
PA000000081	SENSBLUE MONARCH Opaque Case 1 Probe
PA000000082	SENSBLUE MONARCH Opaque Case 2 Probes
PA000000083	SENSBLUE MONARCH Opaque Case 1 Probe External Antenna
PA000000084	SENSBLUE MONARCH Opaque Case 2 Probes External Antenna
PA000000020	SENSBLUE MONARCH RS485 Probe Splitter Box (1 input -> 2 outputs)

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10. Applicable certifications and standards

EMC Directive 2014/30/EU.

EN IEC 61326-1: 2021
EN 55011: 2016+A2: 2021
EN IEC 61000-3-2: 2019+A1: 2021
EN 61000-3-3: 2013+A2: 2021