Table of Contents .......................................................................................................................................... 2
3 General ................................................................................................................................................. 9
3.1 Power Supply ................................................................................................................................... 9
8 Technical Data ................................................................................................................................... 22
The ROTRONIC low-dewpoint probe is designed to measure trace moisture in the range of
-70 .. 85° C (-94 .. 185 °F)T
temperature sensor, and the high-precision AirChip4000 measurement electronics for evaluation and
processing of the sensor data. The probe is designed for dewpoint/frostpoint measurements in compressed-air
systems. The robust stainless-steel housing and the stainless-steel sinter filter make the probe suitable for
industrial applications. The output signals from the low-dewpoint probe are exclusively digital. Suitable devices
for making the dewpoint/frostpoint and temperature measurements available as analog signals are the
ROTRONIC measurement converters in the HF5, HF8 and PF4 series, as well as the ROTRONIC HP22 and
HP23 hand-held meters. Alternatively, the probe can be connected directly to a PC USB port, and read out
using MS Windows HW4 software.
The low-dewpoint probe has the following features:
• Very high precision measure m ent of dew point, fro stpo int and temper atur e
• Pressure-resistant to 100 bar
• Absolute repeatability guaranteed
• The latest AirChip4000 measurement technology
• HYGROMER® LDP-1 sensor
• Software-based sensor alarm function
• Adjustment by customer possible
• 1-point temeparture calibration / adjustment
• Multi-point dew point calibration / adjustment
The units in the LDP series can be kept up to date with regard to improvements in functionality through simple
update of the firmware.
. The dew point probes are based on a capacitive trace moisture sensor, a Pt1000
This manual applies to LDP series probes with firmware vers ion V1.5. T he low-order dig it of the fir mware versio n
stands for minor changes, e.g. correction of errors which do not influence the main functionality of the device.
1.2 Background Information on the Principle of Measurement
The presence of liquid water is undesirable in many ind ustr ial gase s (e.g. compressed air). I t can lea d to rust in
the piping and functional elements, rupture of lubricant films, electrochemical formation of elements, microbial
contamination, and icing , with the associated da mage to the system. I f the dewpoint of the pr ocess gas is known,
a suitable drying pro ce ss ca n be u sed to lower its (pressure) dewpoint to a point at which the formation of liquid
water (condensation) is avoided. By and large, it can be said that the lower the temperature and humidity of a
gas is, the lower its pressure dewpoint will be. Determining this kind of low dewpoint, especially at high gas
pressure, makes considerable demands on the pressur e res i stan ce, chemical resistance, and resolution of the
humidity probe, and on the processor power necessary for the electronics to convert temperature and gas
humidity to the associated low-dewpoint temperature.
That is why the latest AirChip4000 technology is used in the ROTRONIC low-dewpoint probe. It is based on an
enhancement and power boost to the market-proven, high-precision AirChip3000 technology. Humidity
measurement is effected by the new, capacitive HYGROMER
temperature sensor, it all ows the dewpoint or fro stpoint to be determined precis ely. The AirChip40 00 technology
can ascertain any of over 8,00 0 indiv id ual p oint s, and guarantees a high degree of repea tability. The increased
performance is vital for dewpoint applications, because the slightest variations in the environmental conditions
of the delicate trace moisture climate are very important for the results of measurement.
The firmware of the low-dewpoint probe also has an integrated low-pass filter to effectively reduc e sig nal-noise
interference. The result is a low-dewpoint measurement precision of ±2 K T
-50 .. 20 °C T
Familiar functions of the AirChip3000 technology, such as calibration, adjustment, and compatibility with
ROTRONIC measurement tra nsducers and hand-held m eters, are also avail able i n the AirC hip40 00 te chnology
of the LDP probe.
The dewpoint measurement and its equalization time depend on many factors. ROTRONIC therefore provides
a measurement chamber ( see figures 2, 4, 8 and 9) with a pre-set airflow of 1 l itre per minute at 8 b ar pressure.
In the measurement ch am ber, the probe experiences co nst an t airf low, which allows very fas t , pr e cis e d ewpoint
measurement. The equalization time of the measurement value may vary widely between applications. It
depends on the flow velocity in the mea sure men t cha mber, the absolute pressure in the m easurement line, the
dewpoint of the surroundings, and the surface structure of the measurement line.
The measurement chamber is available in POM (polyoxymethylene) or stainless steel. It can be ordered as a
base body or as a ready-assembled unit with a quick-action compressed-air coupling and fixed valve.
Figure 3: Base body of measurement chamber (LDP MC) in POM (polyoxymethylene) and stainless steel.
G1/4“ thread for
customized
connections
compressed-air
G1/4“ thread for
customized
connections
G1/2“ thread for
LDP probe
Fixed valve, airflow
1 litre per min. at 8
bar
G1/2“ thread for
LDP probe
Figure 4: Fully assembled measurement chamber (LDP FC) in POM (polyoxymethylene) and stainless steel.
For full functionality, the LDP probe requires a power supply at 3.3 .. 5 VDC (1.5 mA).
3.2 Measured Parameter s
The ROTRONIC LDP probe calculates the dewpoint/frostpoint from the humidity measurements taken by the
HYGROMER® LDP-1 dewpoint sensor, and temperature measurements from a Pt1000 temperature sensor.
The values for dewpoint, frostpoint and temperature are transmitted in the form of a digital signal.
3.3 UART Interface
The LDP probe has a serial digital UART interface (UART: Universal Asynchronous Receiver Transmitter),
which is compatible to the HF5, HF8, and PF4 measurement transducers, HP22 and HP23 hand-held meters,
and the AC3001 service cable (probe UART to PC U SB). With the HW4 softw are (Professional Vers ion) installed
on the PC, the following functions are available:
• Recording and display of current measur ed and calcul at e d values;
• Configuration of the probe;
• Calibration and adjustment of the probe.
Connect the probe to the PC as follows:
- Connect the LDP probe to a USB port of an MS Windows PC via AC3001 (UART-to-USB adapter).
- Use HW4 to search for and include the unit:
Units and groups > Search for units > Search for USB master
LDP series probes are completely integrated in the HW4 software at V3.4.0 or higher.
3.5 Sensor Filter
The probe must always be protected from soiling by a stainless-steel sinter filter. The filter has a pore size of
50 µm (ROTRONIC Order Code: SP-S15/50).
IMPORTANT:
You should not touch the filter with your bare hands. Soiling of any kind can impair the precision and response
time of the measurements.
• Multi-point dewpoint/frostpoint calibr at ion and adju st ment
Write protection
The device settings can be protected by a password. Password protection is configured with the HW4
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4 User-Specific Settings and Functions
The LDP probe has a large number of functions and settings that users can adapt to suit their requirements.
This chapter contains an overview of all functions and their default settings.
4.1 General AirChip4000 Functions
This section outlines the general functions of the AirChip family available in the LDP probes. All functions can
be used with the HW4 software and are described in detail in the manual E-M-HW4v3-LDP-001.
4.1.1 Calibration and adjustment
• Single-point temperature calibration and adjustment
• Time stamp for each calibration and adjustment point
• Saving and display of the last adjustment data and values
• Creation of a calibration and adjustment log
IMPORTANT:
ROTRONIC recommends that you send the probe back to the manufacturer for calibration and adjustment.
ROTRONIC has a professional, high-quality calibration system that guarantees optimal, certified results.
Specific limit values can be defined for dewpoint, frostpoint and temperature; an alarm is shown in the HW4
Bad sensor alarm
This function is a fixed component of the LDP probe firmware and cannot be disabled. In the case of a short
circuit or power interrupt ion at the dewpoint or temperature sensor , a dig ital a lar m is triggered and displayed
in the HW4 software. While the alarm is pending, the values for dewpoint/frostpoint are set to the current
Automatic threshold monitoring
Threshold monitoring can be enabled or disabled (only with HW4 v3.5).
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4.1.3 Alarm Functions
software when they are exceeded.
The alarm function can be enabled or disabled.
temperature value (e.g. at 23 °C (73 °F), the display shows 23 °C (73 °F) Td).
In the case of a temperature-sensor alarm, the temperature value is set to -99 °C (-146 °F).
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4.1.4 Threshold Monitoring
Enabled: (only if wished by customer this function can be enabled by factory)
Threshold monitoring becomes active below a measured value of -69.9 °C (-94 °F) T
measured value to -66 °C (-89 °F) Td. This allows the user to observe changes in the measured values in
the lower limit range.
Disabled: (default setting)
The value limits integrated in the probe prevent it from measuring values below -70 °C (-94 °F) T
output measurement value is limited at -70 °C (-94 °F) T
There is no static system without any changes. Syst em s are always in motion and thi s m ay must be mon itored.
In this case the threshold monitoring can be used when changes of the value are important even below
-70 °C T
system. After reaching -70 °C Td the value jumps back to -66 °C Td and goes further down until the system is
stable.
. The following graph shows the drying process of a probe after connecting it to a compressed air
d
In this case a compressed air system is monitored which is slightly below -70 °C Td. With the threshold
monitoring activated, variations (e.g.: opening of valves, extensive use of air, leakage, etc.) in the system can
still be seen.
Measured value alarm, invalid measured
Simulator mode
Disabled
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4.2 Factory Defaults
All factory defaults and functions of the LDP probe are described below. The HW4 software (V3.4.0 or higher)
is needed to change them. An AC3001 service cable can be used to connect the probe to the PC.
There are several points to note when choosing the point at which to measure the dewpoint/frostpoint.
5.1.1 Positioning the probe and the measurement chamber
The probe can be screwed dir ectly into a lin e (max. 100 bar), or plugged into a compressed-air connect ion (max.
16 bar) with a measurement chamber (see figure 9).
IMPORTANT: The measurement chamber must not be c onnecte d dir ectly to the compres sed air supply withou t
a properly screwed-in probe, and the probe must not be removed from the measurement chamber when the
chamber is still under pressure.
It is recommended that you position the probe close to the application to be monitored. Long pipelines from the
measurement chamber to the main line that is to be monitored make measurement unnecessarily difficult with
regard to amplitude and r eaction ti me. In order to prevent any drop in environ mental humidi ty and pre ssure fro m
affecting the measuremen ts, there must be no leaks (ex cept for t he o utle t v alv e of the measurement chamber) .
Figure 9: POM measurement chamber LDP-FCPB1 with compressed-air connection (left), probe insertion
thread (right), and fixed valve (top).
5.1.2 Positioning of probe with regard to temperature specifications
Care must be taken that the temperature specifications of the probe are not exceeded by the medium being
measured.
If the temperature is too high, the medium must be cooled down. To avoid condensation, the dewpoint must,
however, be lower than the ambient temperature.
Oil and dust particles in the gas line affect the measurement precision, reaction time and lifetime of the probe.
The probe’s filter cannot filter out particles less than 50 µm in diameter. In this case, it is advisable to install a
more effective external filter upstream. The drop in pressure or reduction in flow volume that this causes can
impair the measurement precision and reaction time. However, the measurement in its steady state would
remain stable over time, even in this setup.
5.1.4 Pressure at the probe head
The maximum permanent pressure for the probe is 100 bar. Please note that the complete measurement
chamber with its quick-action coupling and fixed valve is only approved for up to 16 bar.
The low-dewpoint probe has a ROT RONIC E2 plug that is co mpatible w ith measurement tra nsducers HF5, HF 8,
PF4, HP22 and HP23, and with the AC3001 service cable. Its pin configuration is shown in figure 10.
This chapter describes calibration, adjustment, validation and filter changes as well as the tools necessary for
this, e.g. service cable.
6.1 Service Cable
An AC3001 service cable can be used for m aintenance and calibr ation. T he service cable has an int ernal pow er
supply of 3.3 VDC. Alternatively, the connection to the PC can be made via an HF5, HF8 or PF4 transmitter, or
an HP22/HP23 hand-held meter.
6.2 Calibration
Both the Pt1000-RTD temperature sens or used in the probe and the correspo nding electr onics are ver y stable
and donot normally need to be calibrated after initial factory calibration. The long-term stability of the
HYGROMER
the calibration of the probe s h ould be che ck ed ev ery 12 mo nt hs. A ppl ic atio ns in w hich t he probe is exposed to
considerable contamination could require more frequent checks.
IMPORTANT:
ROTRONIC recommends that you send the probe back to the manufacturer for calibration and adjustment.
ROTRONIC has a professional, high-quality calibration system that guarantees optimal, certified results.
Customers can carry out the adjustments themselves, using the HW4 software.
• Start the HW4 software and look for the connected LDP probe (HW4 Menu > Devices and Groups >
• The device tree of the LDP probe lists all calibration and adjustment functions.
• At least 2 calibration points must be recorded, if adjustments are to be made at a later date.
• The adjustment points must be recorded in the sequence from dry to moist; the lowest calibration point
• You will find further instructions in the LDP sensor software manual, E-M-HW4v3-LDP-001.
®
LDP-1 sensor from ROTRONIC is normally better than 1.°C Td per y ear. For maximum accuracy ,
Search for Devices > Search for USB Master)
must be at the lower limit of the measurement range, with two further points in the range
The probe should be calibrated at least once a year, and adjusted if necessary. ROTRONIC strongly advises
that you return the probe to t he factory for this. If adjustment on site i s necessary , the probe s hould be readj usted
at the following dewpoint values.
• -60 °C Td (±5 °C Td)
• -10 °C Td (±5 °C Td)
You can add further point s as necess ary. It is advi sable to ad just the pr obe in the ord er fro m dr y dew point value
to humid dewpoint valu e. E n su re t ha t th e probe is in steady st ate a t each dewpoint, i.e. t he mea sur ed dewpoint
value no longer changes.
The equipment needed for adjustment (dewpoint reference, low dewpoint generator) has a decisive influence
on the measuring accuracy of the probe.
Calibration/adjustment can be performed with the HW4 software. Should it be necessary to adjust the LDP
probe, this can be done with the HW4 software. You will find further instructions in the HW4 software manual
E-M-HW4v3-LDP-001 for the LDP probe.
6.3 Probe
It is recommended to carry out maint enanc e on the pr obe at least once a y ear (or , in the case of m easure ment s
in oil-polluted air, every 3 mont hs). T o do t his, rem ove the f ilte r and s ubmit i t to a vi sual in spectio n. Soi led part s,
such as measurement chamber, fixed valve or filter, must be cleaned in an ultrasonic bath and alcohol, or
exchanged. If the sensor is soiled, the probe must be returned to the manufacturer.
IMPORTANT:
The sensor filter must be removed very carefully, because touching the trace moisture sensor can destroy it!
The filter should not be touched with bare hands. Any improper maintenance can lead to a reduction in the
precision of measurements.
The LDP probe firmware can be updated with the HW4 software. Firmware updates are available for
downloading on the ROTRONIC website. Updating the firmware requires that the probe be connected via an
AC3001 service cable to a PC with HW4 software installed on it.
IMPORTANT:
There must be a permanent connection to the computer and a stable power supply during the update process.
Procedure:
• Connect the probe to the service cable, or to an HF5, HF8, PF4, HP22 or HP23.
Remark:
As of 2014, the service cables work with a standard USB driver. Older service cables need a
ROTRONIC USB driver, which is installed on the PC together with the HW4 software. For detailed
information on the ROTRONIC USB driver, see the manual E-M-HW4v3-Main.
• Download the latest LDP probe firmware to your PC from the ROTRONIC website.
• Launch the HW4 software on the PC and search for the LDP probe.
HW4 Main Menu > Devices and Groups > Search for Devices > Search for USB Master / Search for
Ethernet Master
• Select the Update option under Device Manager in the menu
Extras > Firmware Update
For further information, see the manual E-M-HW4v3-LDP-001.
All accessories for ROTRONIC products are to be found in the manual E-M-HC2-accessories. The main
service cables for the LDP probe are also listed there:
Order Code Description
LDP-MCP
LDP-MCS
Measuring chamber base body,
POM
Measuring chamber base body,
stainless steel
LDP-FCPB1
LDP-FCSB1
AC4001-B
Measurement chamber with
fixed coupling and quick-action
compressed-air coupling, POM
Measurement chamber with
fixed valve and quick-action
compressed-air coupling,
stainless steel
V1_00 November 2014 Release document
V1_01 November 2014 Graphic of threshold monitoring added
V1_02 March 2015 Response time dry to humid added
V1_03 March 2015 Threshold monitoring is disabled by factory
V1_04 September 2015 Calibration / adjustment specification included
V1_05 November 2015 Chemical compatibility o f LDP-1 sensor added
V1_06 May 2016 Update CE guideline