KISTERS HyQuest Solutions VHPS SDI-12 User manual

Vented Hydrostatic Pressure Sensor
(VHPS): User’s Manual
HyQuest Solutions
-KISTERS Group-
06 JUNE 2020

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Revision Sheet
Release No.
Date
Revision Description
1.0
23 June 2020
First Release

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Content
1SAFETY INSTRUCTIONS .............................................................................................6
2INTRODUCTION ........................................................................................................7
3TECHNICAL DATA......................................................................................................7
4SDI-12 DATA TRANSFER INTERFACE...........................................................................8
4.1 Description ......................................................................................................................... 8
4.2 SDI-12 Command Set........................................................................................................... 8
4.2.1 Data Logger/Controller Commands and Sensor Responses..........................................................8
4.2.1.1 Break..............................................................................................................................................9
4.2.1.2 Acknowledge Active.......................................................................................................................9
4.2.1.3 Change Address Command............................................................................................................9
4.2.1.4 Address Query Command (?!)......................................................................................................10
4.2.1.5 Start Measurement Command ....................................................................................................10
4.2.1.6 Extended Measurements Command ...........................................................................................11
4.2.1.7 Service Request (from sensor to data logger) .............................................................................12
4.2.1.8 Start Concurrent Measurement Command.................................................................................12
4.2.1.9 Start Verification Command ........................................................................................................12
4.2.1.10 Additional Concurrent Measurements Command.......................................................................13
4.2.1.11 Continuous Measurement Command .........................................................................................13
4.2.2 CRC-16 Checksum ........................................................................................................................14
4.2.3 SDI-12 extended commands........................................................................................................14
4.2.3.1 Setting pressure unit....................................................................................................................14
4.2.3.2 Reading pressure unit..................................................................................................................15
4.2.3.3 Setting recalibration value of zero-point pressure......................................................................15
4.2.3.4 Reading recalibration value of zero-point pressure ....................................................................15
4.2.3.5 Setting recalibration value of nominal pressure..........................................................................16
4.2.3.6 Reading recalibration value of nominal pressure........................................................................16
4.2.3.7 Setting temperature unit.............................................................................................................16
4.2.3.8 Reading temperature unit ...........................................................................................................17
4.2.3.9 Setting user identification string..................................................................................................17
4.2.3.10 Reading user identification string................................................................................................18

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4.2.3.11 Saving settings in flash memory ..................................................................................................18
5RECALIBRATION...................................................................................................... 18
5.1 Zero-point pressure recalibration ...................................................................................... 18
5.2 Nominal pressure recalibration ......................................................................................... 19
5.3 Zero-point and nominal pressure recalibration .................................................................. 20
6UNIT CONVERSION .................................................................................................21
7CONTACT DATA ......................................................................................................22
7.1 Australia........................................................................................................................... 22
7.2 New Zealand..................................................................................................................... 22
7.3 Europe.............................................................................................................................. 22
7.4 Latin America.................................................................................................................... 22
7.5 North America .................................................................................................................. 22

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Glossary
ACRONYM
Description
A
SI unit symbol for “Ampere”, physical unit for electrical current
ASCII
American Standard Code for Information Interchange
DB
Data Byte
DW
Data Word
mm
SI unit symbol for “millimetre”, metrical system
P
Pressure
PN
Nominal pressure
PZP
Zero-point pressure
SI
International System of Units
T
Temperature
PN
End of temperature range
PZP
Start of temperature range
SDI-12
A Serial-Digital Interface Standard for Microprocessor-Based Sensors as described in the SDI-12 specifications
http://www.sdi-12.org
VDC
Direct Current
W
SI unit symbol for “Watt”, physical unit of power
ZP
Zero Point
@
at

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1Safety Instructions
•Read the user manual including all operating instructions prior to installing, connecting and pow-
ering up the HyQuest Solutions VHPS. The manual provides information on how to operate the
sensor system. The manual is intended to be used by qualified personnel, i.e. personnel that has
been adequately trained, is sufficiently familiar with installation, mounting, wiring, powering up
and operation of radar sensors.
•Keep the user manual at hand for later reference!
•If you encounter problems understanding the information in the manual (or part thereof), please
consult the manufacturer or its appointed re-seller for further support.
•The manual provides information on how to operate the sensor system.
•Do not use the HyQuest Solutions VHPS in areas where there is a danger of explosion.
•The present user manual specifies environmental/climatic operating conditions as well as me-
chanical and electrical conditions. Installation, wiring, powering up and operation the HyQuest
Solutions VHPS must strictly comply with these specifications.
•Never make any electrical or mechanical diagnostics, inspections or repairs under any circum-
stances. Return the sensor to the manufacturers named repair centre. You can find information
on how to return items for repair in the relevant section of the HyQuest Solutions web site.
•Disposal instructions: After taking the HyQuest Solutions VHPS out of service, it must be disposed
of in compliance with local waste and environmental regulations. The HyQuest Solutions VHPS is
never to be disposed in household waste!

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2Introduction
Thank you for opting for HyQuest Solutions’Vented Hydrostatic Pressure Sensor (VHPS)!
The VHPS SDI-12 provides the following functions:
•Zero-point and nominal pressure recalibration
•SDI-12 interface
•Pressure units selectable
•Temperature units selectable
•Additional identification string
Vented Hydrostatic Pressure Sensors are typically used to measure water levels in running or standing
water bodies. The integration with a data logger –for instance a data logger of the HyQuest Solutions iRIS
family of data loggers –is easy thanks to the sensor’s SDI-12 interface (Version 1.3).
The VHPS measures both water pressure and water temperature. The readings are available via SDI-12
commands. The water temperature is also internally used to provide for a temperature compensated
pressure reading. The VHPS is a vented sensor ensuring natural barometric pressure compensation.
Depending on the actual deployment of the sensor, VHPS can be ordered with either stainless steel or
titanium housing. Likewise, a choice of PUR, PE (for drinking water) and TFE (Teflon impregnated for con-
taminated waters) cables is available.
The present manual describes the common features of all VHPS sensors.
3Technical Data
Table 1 provides an overview on the major specifications of the VHPS Vented Hydrostatic Pressure Sensor.
Table 1. VHPS Specifications
Parameter
MIN
TYP
MAX
Unit
Communication interface: SDI-12
1200
V1.3
1200
bps
Power supply voltage
8.0
12.0
30.0
V DC
Max Current
< 0.5
< 6
mA
Operational Temperature Range
-5
+80
°C
Pressure Measurement range
5
20
10
250
mH2O
mH2O
Pressure Resolution
0.01
% FS
Pressure Measurement Accuracy
≤ ± 0.1
± % FS
Temperature Measurement Range
-25
+85
°C
Temperature Resolution
0.05
°CS
Accuracy Temperature Measurement
≤ ± 0.3
≤ ± 0.5
°C
Pressure Resolution
0.01
% FS
Ingress Protection Rating
IP68
---
Mechanical
Ø24 x H157
Ø0.95 x H6.18
mm
inch

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4SDI-12 Data Transfer Interface
Table 2 –SDI-12 Interface Specs
Protocol
SDI-12, Version 1.3
Default Address
0 (factory settings)
Transfer Rate
1200 baud
Start Bits
1
Data bits
7
Parity
1 bit, even
Stop Bit
1
4.1 Description
SDI-12 is a standard for interfacing data recorders with microprocessor-based sensors. SDI-12 stands for
serial/digital interface at 1200 baud. SDI-12 is intended for applications with the following requirements:
•Battery powered operation with minimal current drain, max. 420mA@12V
•Bus operation: use of a single data recorder with multiple sensors on one cable; each of these
devices must be identified with a unique address, which is represented by a single ASCII char-
acter; if several units connected through the same physical SDI-12 bus must have a distinct
address
•Power is supplied to the sensors through the physical wires of the SDI-12 interface
Figure 1 –SDI-12 Bus (source: http://www.sdi-12.org/current_specification/SDI-12_version-1_4-Jan-10-2019.pdf)
4.2 SDI-12 Command Set
The SDI-12 command implementation is compliant with SDI-12 Specification 1.3.
4.2.1 Data Logger/Controller Commands and Sensor Responses
The following sections describe the basic commands and extended SDI-12 commands implemented in
VHPS sensors. For each command, and where appropriate, the responses provided by the sensor is de-
scribed. SDI-12 is a bi-directional communication protocol. Typically, sensors act as clients providing an-
swers to commands received from a data acquisition device. A data logger or controller sends commands
to the sensor.
SDI-12 commands send by a data-acquisition device or intelligent controller use the same base structure:

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•the sensor address –denoted ‘a’ with a value range [0 …9, A …Z, a …z]
•the character "!" terminates the command
•most commands have a command character
Caution: The address character "?" can only be used if only a single sensor is connected to the physical
SDI-12 bus. All sensors on the bus will respond to the “?” address character.
All responses sent after a command has been received and processed use the same base structure:
•the address, and
•the character chain “<CR><LF>” to terminate the answer.
•most responses also contain data with or without a CRC-16.
4.2.1.1 Break
A break is sent to wake up the sensor(s). Sending a break command ensures that all sensors on the bus
will wake up and prepare to be ready to not miss the commands that follow. A break is a constant bus
level (spacing) for 12 ms.
4.2.1.2 Acknowledge Active
This command ensures that the addressed sensor responds to the data logger. This command has no
command character.
•Command: a!
•Response: a<CR><LF>
With a == the sensor address (0, 1..9, A..Z, a..z)
4.2.1.3 Change Address Command
Change/set the address of a connected sensor. The factory default address of each sensor is "0".
Caution: To avoid addressing conflicts on the bus, each sensor must have its unique address on the bus.
Preferably, the unique address is different from the default address. If two or more sensors on the same
bus share the same address, address conflicts will arise making the bi-directional SDI-12 communication
impossible.
•Command: aAb!
•Response: b<CR><LF>
where:
•a old sensor address (0, 1..9, A..Z, a..z)
•b new sensor address (0, 1..9, A..Z, a..z)
Example Change Address Command (aI!)
Changing the Address from “0”to “1”
•Command: 0A1!
•Response: 1<CR><LF>
Changing the Address from “1”to “0”
•Command: 1A0!

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•Response: 0<CR><LF>
4.2.1.4 Address Query Command (?!)
This command queries the sensor address. Using the generic ‘?’ address, forces all sensors connected to
the bus to respond. It must be noted that if more than a single sensor is connected to the bus, they will
all respond, causing a bus contention. However, to comply with the SDI-12 standard, each sensor is re-
quired to support the wild card address character (?) with the acknowledge active command (?!).
•Command: ?!
•Response: a<CR><LF>
where:
•a == sensor address (0, 1..9, A..Z, a..z)
4.2.1.5 Start Measurement Command
To keep power consumption low, SDI-12 sensors hibernate between measurements. The Start Measure-
ment command wakes up the sensor and tells it to take a measurement. The VHPS will start measuring
both pressure and temperature. In compliance with the SDI-12 standard, the sensor responds providing
two bits of information:
•the number of measurements ‘n’ in the valid range 1 to 9 (in the case of the VHPS, n=2), and
•the time ‘ttt’ until these two measurements will be ready.
Note that SDI-12 sensors will not provide the actual measurement unless they receive send data command
(D0!). If the sensor has the measuring results available before the specified time expires, then it sends a
Service Request (see 4.2.1.7) to the data logger.
•Command: aM! Requesting measured values without CRC-16 checksum
aMC! Requesting measured values with CRC-16 checksum
•Response: atttn<CR><LF>
where:
•a == sensor address (0, 1..9, A..Z, a..z)
•ttt == time in seconds until measurements/readings are available
•n == no. of measured data (0..9)
n = 2 (One pressure and one temperature measured value in the case of the VHPS)
After the M command and before the sensor issues the service request, the data recorder may not com-
municate with any other sensor. The sensor must not drive the data line until it sends a service request.
The recorder must not drive the data line while waiting for the service request.
Examples Get Measurement
•Command: 0M! (start measurement)
•Response: 00012<CR><LF> (2 measurements ready in 1 second)
•Response: 0<CR><LF> (Service Request)
•Command: 0D0! (send data)
•Response: 0+0.012-1.3<CR><LF> (e.g. +0.012bar, -1.3°C)