TEKBOK TBSHT06,TBSHTP06 SDI-12 Air Humidity, Temperature and Barometric Pressure Sensor Owner’s Manual

TEKBOX TBSHT06, TBSHTP06 SDI-12 Air Humidity, Temperature, and Barometric

Pressure Sensor

The TBSHT(P)06 is an air humidity and temperature sensor with an SDI-12 interface. The sensor uses a single chip sensor element which measures both temperature and air humidity. An additional, optional MEMS chip measures barometric pressure. Each sensor chip is individually factory-calibrated.

The TBSHT06/TBSHTP06 PCB assembly is silicon cast inside the sensor housing. A replaceable PTFE filter cap with a 10µm pore diameter provides dust and insect protection. The sensor has a length of 100mm and a diameter of 16mm.
The sensor can be supplied as an air temperature / relative humidity variant with part number TBSHT06 or as a temperature / relative air humidity /barometric pressure sensor with part number TBSHTP06.

Features

• Air humidity, temperature, and barometric pressure sensor
• SDI-12 Interface
• Digital temperature sensor: ±0.2°C (range: 0 – 90°C)
• Air humidity sensor tolerance: ±2%RH (range: 0 – 100%)
• Barometric pressure sensor tolerance:: ±0.5hPa (range: 300-1250hPa)
• Replaceable PTFE filter cap, 10µm
• SDI-12 Standard V1.3
• 6 – 17V supply voltage
• Power consumption:
• Active: 8 mA
• Idle: 24µA
• Operating Temperature Range: – 40°C … + 85°C
• Dimensions: 100 mm x 16 mm
• Target Applications
• SDI-12 Sensor Networks

Introduction

Note: this user manual is relevant only to TBSHT06 and TBSHTP06 products which have their FW version starting with 16 (TBSHT06) or 17 (TBSHTP06) For other FW versions, refer to user manual v1.3.

Checking TBSHT06/TBSHTP06 FW version:

• Send 0I!
• Response:
  • TBSHT06: 013TBSHT6rvD1234561600103 => TBSHT06 FW version 16.0.xx.xx
  • TBSHTP06: 013TSHTP6rvD1234561700103 => TBSHTP06 FW version 17.0.xx.xx

Product Features
TBSHT06/TBSHTP06 is based on factory-calibrated sensor chips, a low-power controller, and robust SDI-12 interface hardware:

• Measurement of air humidity, air temperature, barometric pressure (optional), and calculation of absolute air humidity, dew/frost point
• 5V, 1200 baud SDI-12 data interface with transient protection
• Power supply: 6 – 17V, current: 8 mA (active) / 24µA (idle)
• Sensor dimensions: 100 mm, Ø 16 mm
• Operating temperature range: -40°C … +85°C

Calibration

• Each sensor is individually factory-calibrated. No further user calibration is required.
• Nevertheless, for some specific conditions, additional temperature calibration methods are available.
• The different options are further described in a dedicated chapter.

Placement
Don´t expose the sensor to direct sun or precipitation. Install it in a location with permanent shadow and protection from precipitation, inside a radiation shield, or in an instrument shelter.

Installation
The TBSHT06/TBSHTP06 is compatible with any data logger or remote telemetry unit with an SDI-12 interface. Refer to the data logger or RTU manual and Chapter 2 of this datasheet. The sensor is equipped with a PTFE filter cap with a pore size of 10 microns. It is advised to replace the filter cap every year.

SDI-12
SDI-12 is a standard for interfacing data recorders with microprocessor-based sensors. SDI-12 stands for serial/digital interface at 1200 baud. It can connect multiple sensors with a single data recorder on one cable. It supports up to 60-meter cables between a sensor and a data logger. Tekbox SDI-12 sensors have been installed in networks with cable lengths up to 200m and with up to 40 connected sensors.

The SDI-12 standard is prepared by the SDI-12 Support Group
(Technical Committee)

• 165 East 500 South
• River Heights, Utah
• 435-752-4200
• 435-752-1691 (FAX) http://www.sdi-12.org

The standard is available on the website of the SDI-12 Support Group. More information on SDI-12 is presented in Chapter 3.

Application Examples
Figure 1 – TBSHT06/TBSHTP06 sensors connected to TBS03 SDI-12 to USB converter, setup for controlling/testing sensors and for PC-based data recording.

Functional Description

Overview
The SDI-12 standard defines a set of commands to configure sensors and initiate measurements. Upon receiving specific commands, the sensor may carry out internal tasks, respond with information on conversion time, or send measurement data.

SDI-12 commands are typically ASCII strings that are generated by the data recorder/controller firmware. The TBSHT06/TBSHTP06 can be connected to a TBS03 SDI-12 to USB converter and controlled by a PC application or HyperTerminal. TBS03 converts the command strings to the logic levels and baud rate specified by the SDI-12 standard. Furthermore, TBS03 handles breaks, marks, and all other details of the SDI-12 protocol.

Upon receiving data or status information originated by the TBSHT06/TBSHTP06, the TBS03 extracts the corresponding ASCII strings and sends them to the USB Virtual COM Port of the PC. In remote applications, the TBSHT06/TBSHTP06 can be connected to a data logger, a data terminal, or a Radio Telemetry Unit with an SDI-12 interface.

SDI-12 Basics
The SDI-12 is a serial data communication standard for interfacing multiple sensors with a data recorder. SDI-12 uses a shared bus with 3 wires: power (+12V), data, and ground Data rate: 1200 baud. Each sensor at the bus gets a unique address which is in the range ASCII [0-9, a-z, A-Z]. The default address of every sensor is ASCII[0]. When setting up an SDI-12 sensor network, every sensor needs to be configured with a unique address. This can be done using the Change Address Command. A sensor can typically measure one or more parameters. Sensor manufacturers

usually specify ‘Extended Commands’ to configure or calibrate sensors. These commands are specified by the manufacturer, but they follow the command structure specified by SDI-12. A typical recorder/sensor measurement sequence proceeds as follows:

1. The data recorder wakes all sensors on the SDI-12 bus with a break.
2. The recorder transmits a command to a specific, addressed sensor, instructing it to make a measurement.
3. The addressed sensor responds within 15.0 milliseconds, returning the maximum time until the measurement data is ready and the number of data values it will return.
4. If the measurement is immediately available, the recorder transmits a command to the sensor instructing it to return the measurement result(s). If the measurement is not ready, the data recorder waits for the sensor to send a request to the recorder, which indicates that the data is ready. The recorder then transmits a command to get the data.
5. The sensor responds, returning one or more measurement results.

SDI-12 Command Structure
Each SDI-12 command is an ASCII string with up to 5 characters, starting with the sensor address and terminated by a “!” character.

Example
Send Identification Command 0I!

• is the sensor address (sensor zero). Upon receiving this command, the sensor will send an ASCII string containing the sensor address, SDI-12 compatibility number, company name, sensor model number, sensor version number, and sensor serial number.

The standard process to carry out a measurement is to send a measurement request upon which the sensor responds with the time that is required to carry out the measurement and the number of data items being returned. After waiting for the time that the sensor requires to carry out the measurement, the data recorder sends a “Read Command” to get the measurement results.

Example
Start Measurement Command 0M! Sensor 0 may respond 00053 which means the sensor will take 5 seconds to deliver 3 measurement values. After min. 5 seconds, the data recorder can send the “Read Data Command” 0D0! to which Sensor 0 replies 0+68.83+25.29+19.1626. +68.83+25.29+19.1626 are the three measurement results corresponding to air humidity (68.83), air temperature (25.29), and dew point (19.1626). The response string of a sensor is always in ASCII format and may contain up to 40 or up to 80 characters, depending on the type of command. Out of 40 or 80 characters, the values part of the response string may contain up to 35 or 75 characters.

Sensor Identification
The air humidity temperature sensor interface will respond with a string of the following format when sending the “Send Identification” command aI!: alcove X Example: 013TEKBOXVNTSHTP6rvD1234561700100 Where: 0 SDI-12 Sensor address 13 SDI-12 version number, version 1.3 TEKBOXVN Company name TSHTP6 Model Name rvD HW version 123456 Serial number 1700100 FW version Remark about the model name field me:
For TBSHTP06: M is TSHTP6

For TBSHT06: M is TBSHT6 3.4 Sensor Address Each TBSHT06/TBSHTP06 is delivered with a default address of “0” The TBSHT06/TBSHTP06 accepts SDI-12 addresses in the range “0” to “9”, “A” to “Z” and “a” to “z”. Setting the TBSHT06/TBSHTP06 address can be done using the “Change Address Command” aAb!.

Note

• If the new address is invalid, the current address will be kept.
• The TBSHT06/TBSHTP06 will remain unresponsive for approximately 1 second while the new address is saved in the EEPROM memory.
• The TBSHT06/TBSHTP06 interface supports “?” as an address only for “Acknowledge Active”

Command a!.

Measurement
The TBSHT06/TBSHTP06 sensor interface accepts the “Start Measurement” Command aM!, “Additional Measurement” Commands aMn! and “Start Concurrent Measurement” Command aC!, “Additional Concurrent Measurement” Commands aCn! for obtaining calibrated values from the probe.

The TBSHT06/TBSHTP06 sensor interface will not support the “Continuous Measurement” Command aRn! and “Continuous Measurement and Request CRC” Command aRCn!. The TBSHT06/TBSHTP06 sensor will respond with its address followed by in response to this command. The response to “Start Measurement” aM!, “Additional Measurement” Commands aMn! and “Start Concurrent Measurement” Command aC!, the “Additional Concurrent Measurement” Command aCn! reports how many sensor values will be sent.

To receive the desired sensor values, the recorder needs to issue the corresponding “Send Data” Command(s) aDn!.
Note: The TBSHT06/TBSHTP06 sensor interface uses a format of “sign” followed by n digits (The n maximum is seven -7), followed by the decimal point, followed by m digits (The m maximum is one – 1) (+n.m) return readings.

Commands – Quick Reference

Measurement commands
(*): TBSHTP06 only Extended SDI-12 commands: aXC! Set temperature unit to Celsius (default factory setting) aXF! Set temperature unit to Fahrenheit aXM! Select the measurement mode axles! Set the custom calibration parameters and coefficients aXLG! Get the custom calibration parameters and coefficients.

Commands| Parameters| Units| Example: measurements returned by 0D0! (TBSHTP06)
---|---|---|---

aM!      aMC!    aC!       aCC!

| Relative humidity, Air temperature, Dew/Frost point,

Barometric pressure(*)

| %

°C / °F

°C / °F

hPa

|

0+68.83+25.29+19.1626+1006.53

aM1!     aMC1! aC1!     aCC1!

| Absolute humidity,

Cloud base, Altitude(*)

| g/m3 m

m

|

0+16.14+748.433+58.2094

Parameters

Measured parameters
Only 3 parameters are measured while others are calculated from these values.

Refer to the technical specification for further details.

Calculated parameters
Given the below-measured parameters:

• RH: relative humidity [%]
• T: temperature [°C] (TK: temperature in Kelvin [K])
• PB: barometric pressure [hPa]

The following parameters are estimated

• TD: dew point temperature [°C]

• PV: vapour pressure [hPa]

• PVsat: saturated vapor pressure [hPa]

• CE: estimated cloud base [m]

• AH = absolute humidity in g water vapor per m3 of air

• He: estimated altitude [m] Using the following formulas (these are given for reference only as there are many different implementations available depending on the environment and expected tolerance):

• Saturated vapor pressure
  It is calculated based on Teton’s formula for temperature equal to or above zero degrees Celcius:

  • PVSat = 6.1078 * e17.27T/(T+237.3)
  • And the Murray’s variant is applied for negative temperatures:
  • PVSat = 6.1078 * e21.87T/(T+265.5)

Vapor pressure
PV = (RH /100) * PVsat

Dew point (Temperature ≥ 0) / frost point (Temperature < 0)
TD = (b * α(T, RH)) / (a – α(T, RH))

Where
α(T, RH) = ln(RH/100) + aT/(b+T)
a=17.625 and b=243.04 are the Magnus coefficient values as recommended by Alduchov and Eskrige.

Absolute humidity
Temperature in Kelvin: TK = T + 273.15

AH = 105

• (MW / R) (PV / TK)

Where

• R*
• = 8314.3 J/(kmol*K) (molar gas constant)
• MW = 18.016 kg (molecular weight of water vapor)

Estimated cloud base
CE = (T-TD) * 122

Estimated altitude
From the barometric pressure formula, the estimated altitude is

Where

• P0 = 1013.25 hPa (pressure at sea level)
• R = 8.31432 N.m/(mol.K) (universal gas constant)
• M = 0.0289644 kg/mol (air molar mass)
• g = 9.81 m/s2 (acceleration due to gravity)
• P: pressure [hPa]
• TK: temperature [K]

Temperature calibration
TBSHT(P)06 uses a digital IC sensing element to measure the temperature, which ensures a typical tolerance of ±0.2°C over 0°C to 90°C. However, the use of a protective PTFE filter cap impacts the actual temperature measurement tolerance depending on ambient conditions. TBSHT(P)06 has then been finely tuned to achieve the following tolerance: ±0.50 °C when the temperature is between -20 °C to 60 °C. These are the default factory settings that are applied.

The external command XM allows switching between different measurement modes:

• Raw values: in that mode, no calibration is applied to the temperature measurements Command: XM0!
• Custom calibration: in this mode, it is possible to define a custom calibration to be applied on top of temperature raw measurements by using the extended command XLS Command: XM1!
• Factory calibration: this is the default embedded temperature calibration described above. Command: XM2!
• When the custom calibration is enabled with XM1!, a 2-level custom calibration for temperature measurement can be configured by using the XLS extended command (however it’s also possible to apply just one calibration method).
• different calibration methods are available on top of temperature raw values over the [TMin; TMax] operating range:
  • Method (O) – Offset: TMeas = Traw + Offset
  • Method (L) – Linear: TMeas = aTraw + b
  • Method (A) – Percentage: TMeas = Traw−
  • This method is not a calibration per se but rather a conversion to a percentage within a defined range for cases where a temperature ratio is preferred.
• Method (P) – Polynomial: TMeas = aT3 raw + bT2 raw + cTraw + d
• Method (R) – Multi ranges polynomials: same as above but up to 3 polynomials can be applied to 3 different and consecutive temperature ranges covering the whole operating range.

Example
TBSHT06 is deployed in an area where the actual temperature ranges from -10 °C to +25 °C.
The first method applied is multi-polynomials calibration (method R) over 3 temperature ranges:

• Range 0: -10 °C to 0 °C – Polynomial P1 with coefficients a1, b1, c1, d1
  • 0XLS00R-10,0, a1, b1, c1, d1!
• Range 1: 0 °C to 10 °C – Polynomial P2 with coefficients a2, b2, c2, d2
  • 0XLS01R0,10, a2, b2, c2, d2!
• Range 2: 10 °C to 25 °C – Polynomial P3 with coefficients a3, b3, c3, d3
  • 0XLS02R10,25, a3, b3, c3, d3!

The second method applied is an offset compensation (method O) on top of the multi-polynomials calibration:

• Offset applied: -0.03 °C
• 0XLS10O-10,25,-0.03!
• The range index is set to zero as this parameter is relevant only to multi-polynomial calibration
• The method applies to the whole operating range (-10 °C to 25 °C)

Note related to humidity calibration
TBSHT(P)06 measures the air humidity level through a digital IC and does not apply any compensation for this measurement. Would there be a need to adjust the measured humidity, the command XLS2… can be used for that purpose (only one method can be applied in this case). Refer to the technical specification and the extended commands description for further details.

Supported SDI-12 Commands
The following commands are supported by the TBSHT06/TBSHTP06:

aI!

|

Send Identification

| Identification information a13TEKBOXVNrv With:

o    : SDI-12 address

• SDI-12 Support Group
• Tekbox Digital Solutions |

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