Kahn Easidew Plus User manual

Easidew Plus
Portable Hygrometer
User’s Manual
97478 Issue 1
Kahn Instruments, Inc. 2015
This document is the property of Kahn Instruments and may not, either in part or whole, be copied or
otherwise reproduced, communicated in any way to third parties nor stored in any data processing
system, without the written authority of Kahn Instruments, Inc.

Easidew Plus Portable
Hygrometer
For Kahn Instruments' contact information please go to
www.kahn.com

Easidew Plus Portable Hygrometer User’s Manual
Kahn Instruments 3
1 INTRODUCTION ................................................................................................1
2 INSTALLATION ..................................................................................................2
3 OPERATION ......................................................................................................4
3.1 General Operation .............................................................................................. 4
3.2 Measuring Dew Points Below -40°F (-40°C )......................................................... 5
3.3 User Controls ..................................................................................................... 6
3.4 4–20 mA Output Socket Wiring............................................................................ 7
4 GOOD MEASUREMENT PRACTICE .......................................................................8
5 MAINTENANCE ................................................................................................12
5.1 Calibration ....................................................................................................... 12
5.2 Sensor / Battery Replacement ........................................................................... 12
5.3 Filter Cartridge Replacement ............................................................................. 14
5.4 Checking the Easidew Plus Portable Hygrometer Electronics Calibration................ 14
5.5 List of Spares ................................................................................................... 14
5.6 Troubleshooting................................................................................................ 15
Contents
Safety ................................................................................................................................ v
Electrical Safety ........................................................................................................... v
Pressure Safety............................................................................................................ v
Toxic Materials ............................................................................................................. v
Repair and Maintenance ............................................................................................... v
Calibration................................................................................................................... v
Abbreviations......................................................................................................................vi
Warnings ............................................................................................................................vi
Appendices
Appendix A Technical Specications..............................................................................17
Appendix B EU Declaration of Conformity......................................................................19
Figures
Figure 1 Swagelok®Fitting Instructions.....................................................................3
Figure 1A Adaptor Fittings..........................................................................................4
Figure 2 User Controls .............................................................................................6
Figure 3 Jack Plug Wiring.........................................................................................7
Figure 4 2-Wire Connection - View Showing Rear of Connector Terminal Block...........14

Easidew Plus Portable Hygrometer User’s Manual
497478 Issue 1, October 2014
Safety
The manufacturer has designed this equipment to be safe when operated using the procedures
detailed in this manual. The user must not use this equipment for any other purpose than that
stated. Do not apply values greater than the maximum value stated.
This manual contains operating and safety instructions, which must be followed to insure the safe
operation and to maintain the equipment in a safe condition. The safety instructions are either
warnings or cautions issued to protect the user and the equipment from injury or damage. Use
qualied personnel and good engineering practice for all procedures in this manual.
Electrical Safety
The instrument is designed to be completely safe when used with options and accessories supplied by
the manufacturer for use with the instrument. The instrument is powered by an internally mounted
rechargeable battery. The input power supply voltage limits for the battery charger supplied with the
instrument are 90 to 264 V AC, 47/63 Hz.
NOTE: No other battery charger unit, other than that supplied with the instrument
should be used.
NOTE: Do not allow the battery to fully discharge.
Pressure Safety
DO NOT permit pressures greater than the safe working pressure to be applied to the instrument.
The specied safe working pressure is 4350 psig (300 barg). Refer to the Technical Specications in
Appendix A.
Toxic Materials
The use of hazardous materials in the construction of this instrument has been minimized. During
normal operation it is not possible for the user to come into contact with any hazardous substance
which might be employed in the construction of the instrument. Care should, however, be exercised
during maintenance and the disposal of certain parts.
Repair and Maintenance
The instrument must be maintained either by the manufacturer or an accredited service agent. Refer
to www.kahn.com for details of Kahn Instruments’ worldwide ofces contact information.
Calibration
The recommended calibration interval for the Easidew Plus Portable Hygrometer is one year, unless
otherwise specied by Kahn Instruments The instrument should be returned to Kahn Instruments.

Easidew Plus Portable Hygrometer User’s Manual
Kahn Instruments 5
Abbreviations
The following abbreviations are used in this manual:
AC alternating current
atm pressure unit (atmosphere)
barg pressure unit (=100 kP or 0.987 atm) gauge
°C degrees Celsius
°F degrees Fahrenheit
dp dew point
ft feet
kg kilogram
lb pound
mA milliampere
m meter
mm millimeter
MPa megapascal
Nl/min normal liters per minute
psig pound(s) per square inch (gauge)
scfh standard cubic feet per hour
μm micrometer
Ω ohm
V Volts
Warnings
The following general warnings listed below are applicable to this instrument. They are
repeated in the text in the appropriate locations.
!
Where this hazard warning symbol appears in the following
sections, it is used to indicate areas where potentially hazardous
operations need to be carried out.

Easidew Plus Portable Hygrometer User’s Manual
Kahn Instruments 1
INTRODUCTION
1 INTRODUCTION
The Easidew Plus Portable Hygrometer comprises a fast responding polymer sensor
installed into a sample block with an integrated lter cartridge, and Swagelok®tube
ttings on the gas inlet and outlet. The measured dew point from the sensor is shown
on the clear red LED display on the front panel of the instrument.
The Easidew Plus Portable Hygrometer can be supplied with either °C or °F dew-point
measurement units.
A 4-20 mA analog output is provided for connection to a chart recorder, data-logger or
computer system, so dew-point trends can be analyzed over time.
The electronics are housed in a rugged Peli case, providing NEMA 6 protection when the
lid is closed. The case is supplied with a lifetime guarantee.
The Easidew Plus Portable Hygrometer is powered by a rechargeable NiMH battery
pack, giving between 12 and 16 hours of measurement time from a full charge. The
instrument is delivered complete with a universal battery charger stored in the lid.
It takes 16 hours to fully charge the battery pack, during which time the instrument
can be switched on or off. The charger is suitable to connect power to the instrument
indenitely, but it is recommended to allow the battery pack to go through a full charge-
discharge cycle at least once per month. A battery charge indicator on the instrument
front panel warns when the battery is low.
Easidew Plus Portable Hygrometer polymer moisture sensors are subject to a 9-point
calibration, where their performance is characterized against a fundamental reference
hygrometer. This process, and subsequent quality testing, insures that all sensors behave
optimally before they are used in the eld. Each Easidew Plus Portable Hygrometer is
supplied with a calibration certicate traceable to national standards (NIST) from Kahn
Instruments.

Easidew Plus Portable Hygrometer User’s Manual
297478 Issue 1, October 2014
INSTALLATION
2 INSTALLATION
On delivery, please check that all the following standard components are present in the
packing box:
• Easidew Plus Portable Hygrometer
• Swagelok®1/4" metering valve
• Swagelok®1/4" tube port adaptor
• Battery charger
• Power cord
• 3 pole ¼” jack plug (inside lid)
• User manual
• Certicate of calibration
• 0.4mm orice
Before using the Easidew Plus Portable Hygrometer for the rst time it is recommended
that the battery pack is charged for a minimum of 12 hours.
The case has a pressure relief valve on the exterior below the handle. When closed,
the case is completely sealed. If the instrument is taken through altitude changes, a
pressure differential will occur within the case. If this occurs: Before opening the lid,
open the black pressure relief valve by one turn (counter-clockwise) for a few seconds.
This will equalize the pressures. When the case has been opened, insure that the
pressure relief valve has been fully closed.
The supplied Swagelok®port adaptor needs to be assembled before the metering valve
can be connected to the instrument.
See below:
1. Slip the nut over the
machined ferrule end of
the port connector
2. Insert the port connector
into the end connection and
finger-tighten the nut
3. While holding the fitting
body steady, tighten the
nut one-quarter turn
Do not use the Swagelok gap inspection
gauge with machined ferrule ends.
!
1. Slip the nut over the
machined ferrule end of
the port connector
2. Insert the port connector
into the end connection and
finger-tighten the nut
3. While holding the fitting
body steady, tighten the
nut one-quarter turn
Do not use the Swagelok gap inspection
gauge with machined ferrule ends.
!

Easidew Plus Portable Hygrometer User’s Manual
Kahn Instruments 3
INSTALLATION
1. Slip the nut over the
machined ferrule end of
the port connector
2. Insert the port connector
into the end connection and
finger-tighten the nut
3. While holding the fitting
body steady, tighten the
nut one-quarter turn
Do not use the Swagelok gap inspection
gauge with machined ferrule ends.
!
NOTE: Connect the machined ferrule end before
connecting the tube adapter end
4. Insert the tube adapter until it rests firmly on
the shoulder of the Swagelok®tube fitting body.
Finger-tighten the nut.
5. Mark the nut at the 6 o’clock position. While holding
the fitting body steady, tighten the nut 1¼turns to the
9 o’clock position.
NOTE: Connect the machined ferrule end before
connecting the tube adapter end
4. Insert the tube adapter until it rests firmly on
the shoulder of the Swagelok®tube fitting body.
Finger-tighten the nut.
5. Mark the nut at the 6 o’clock position. While holding
the fitting body steady, tighten the nut 1¼turns to the
9 o’clock position.
Figure 1 Swagelok®Fitting Instructions

Easidew Plus Portable Hygrometer User’s Manual
497478 Issue 1, October 2014
OPERATION
3 OPERATION
!
Maximum operating pressure is 4350 psig (300 barg).
It is important that the gas ttings are correctly tightened, and
any tubing is secure in the push ttings before use.
Failure to do so will affect the instrument's pressure rating.
3.1 Instrument Gas Connections
Sample gas connections are made via the Gas in and Gas out ports located on
the front of the instrument. Each of these ports is equipped with an adaptor (3) which
screws into each gas port.
Two types of adaptors are supplied; a small bore orice to allow sample gas either in
or out of the instrument and two larger bore orices. Both types of adaptor have a ⅛”
NPT internal thread to accommodate the customer’s choice of Gas input and Gas output
connection ttings.
A range of connection tting options is available.
Depending upon whether measurements are to be taken at atmospheric pressure
or line pressure, the adaptors need to be installed as shown in Figure 1A.
Readings at atmospheric
pressure
Readings at line pressure
System pressures from 15-150
psig (1-10 barg)
Inlet: Small Orice (#2) Inlet: Large orice (#1)
Outlet: Large Orice (#1) Outlet: Small Orice (#2)
System pressures from 150-350
psig (10 - 300 barg)
Large orice (#1)
Small orice (#2)
Figure 1A Adaptor Fittings
3.2 General Operation
To operate the Easidew Plus Portable Hygrometer, follow these instructions:
1. Insure that both the gas ttings and the Swagelok® tube ttings are fully
tightened before use.
2. For measurement at low pressure or atmospheric pressure, no valving is
necessary.
3. For measurement at high pressure (150 psig to 4350 psig / 10-300 bar),
connect the supplied metering valve to the outlet of the instrument.
4. Gas under test should be restricted to ow rates 2 and 10 scfh (between
1 and 5 Nl/min) and pressures from atmospheric to 4350 psig (300 barg).
5. Connect the sample gas supply line to the instrument Gas In port.
6. Connect the sample gas vent line to the instrument Gas Out port.

Easidew Plus Portable Hygrometer User’s Manual
Kahn Instruments 5
OPERATION
7. Switch the instrument on. The display will begin to change as the sensor
responds to the applied dew point.
8. Allow the gas to ow until the display shows a stable reading. Typically
this would be around 15 to 30 minutes for spot checks at dew points of
-40°F (-40°C ) and above.
9. Switch the unit off and disconnect the sample lines.
!Before disconnecting the Easidew Plus Portable Hygrometer
from the gas line it is essential to vent the system to
atmospheric pressure, otherwise severe injury could result.
NOTE: Filters are essential for potentially dirty/contaminated gases – the
installed lter should be checked before and after use and replaced regularly
- as required.
3.3 Measuring Dew Points Below -40°F (-40°C )
Due to the signicantly lower levels of moisture present at dew points of this level, and
the increased amount of time to dry the system out, the response times of the sensor
will be signicantly increased. The table below offers an approximate guide to the
times taken for the instrument to stabilize at a given dew point (from a starting point
of 10°Cdp (50°Fdp) ambient):
Target Dew Point T100 Response Time
(mins)
°F °C
-22 -30 5
-40 -40 15
-58 -50 30

Easidew Plus Portable Hygrometer User’s Manual
697478 Issue 1, October 2014
OPERATION
3.4 User Controls
°Cdp
Power Fuse
4-20
mA
O/P
Battery
Level
Battery
Charger
To measure
at
line
pressure
atmospheric
pressure
Gas Out Gas In
2 1
21




o
-
BATTERY
Gas Out Gas In
Filter Fitted
2
13 4
5
6
7

 





Figure 2 User Controls
1 Digital Display
Indicates the measured dew point in °F or °C from -58 to +68°F
(-50 to +20°C).
Under certain conditions the following error messages may be
displayed:
ErrL = Sensor under range
ErrH = Sensor over range
Err I = Sensor fault or sensor disconnected
2 Power Switch Switches the Easidew Plus Portable Hygrometer ON or OFF.
3 Fuse
This 1A quick blow fuse provides protection for the display
electronics in the event of a fault with the charger or battery
pack. Another protection fuse is located on the display PCB.
4NiMH Battery
Pack
Located in the top right hand corner of the instrument, it can be
accessed by removing two screws (5). The battery pack can be
recharged using the supplied charger, via the battery-charging
socket and should be recharged whenever the battery level
meter is in the red region. See Section 5.6 for troubleshooting
information.
The battery pack will charge if the instrument is switched ON or
OFF. However, the battery level meter will only indicate when
the instrument is switched on.
6Analog Output
Socket
The Easidew Plus Portable Hygrometer features an analog
output socket that provides a linear 4-20 mA current loop,
scaled to -76 to +140°F (-60 to +60°C) dew point. This allowed
the instrument to be connected to a chart recorder, data logger
or PC to enable dew-point trends to be analyzed over time.
7 Gas Fittings
The Easidew Plus Portable Hygrometer can be used for
measurements at line pressure (up to 4350 psig (300 barg))
or atmospheric pressure. Swagelok® tube ttings are supplied
for use with 1/4" OD stainless steel tube. There is a 32mm
particulate lter (99.5% removal of 0.1 micron particles)
installed as standard under the Gas In port position.

Easidew Plus Portable Hygrometer User’s Manual
Kahn Instruments 7
OPERATION
3.5 4–20 mA Output Socket Wiring
The Easidew Plus Portable Hygrometer provides a linear 4-20 mA output scaled from
-76 to +140°F (-60 to +60°C).
The socket accepts a 3 pole ¼” jack plug (supplied) and should be wired as shown
below:
-VE
-VE
+VE
+VE


 
Figure 3 Jack Plug Wiring

Easidew Plus Portable Hygrometer User’s Manual
897478 Issue 1, October 2014
GOOD MEASUREMENT PRACTICE
4 GOOD MEASUREMENT PRACTICE
Measurement of moisture content is a complex subject, but does not need to be difcult.
This section aims to explain the common mistakes made in measurement situations, the
causes of the problem, and how to avoid them. Mistakes and bad practices can cause
the measurement to vary from the expectation; therefore a good sampling technique is
crucial for accurate and reliable results.
Transpiration and Sampling Materials
- 20
- 30
- 40
- 50
- 60
- 70
12345
Time (hours)
Dew point (ºC)
nylon
copper
polyethylene
PTFE
nickel
stainless steel
All materials are permeable to water vapor, as the water molecule is extremely small
compared to the structure of solids, even when compared to the crystalline structure of
metals. The graph to the right shows the dew point inside tubing of different materials
when purged with very dry gas, where the exterior of the tubing is in the ambient
environment.
Many materials contain moisture as part of their structure, particularly organic materials
(natural or synthetic), salts (or anything which contains them) and anything which
has small pores. It is important to insure that the materials used are suitable for the
application.
If the partial water vapor pressure exerted on the outside of a compressed air line is
higher than on the inside, the atmospheric water vapor will naturally push through the
porous medium causing water to migrate into the pressurized air line. This effect is
called transpiration.

Easidew Plus Portable Hygrometer User’s Manual
Kahn Instruments 9
GOOD MEASUREMENT PRACTICE
Adsorption and Desorption
Adsorption is the adhesion of atoms, ions, or molecules from a gas, liquid, or dissolved
solid to the surface of a material, creating a lm. The rate of adsorption is increased at
higher pressures and lower temperatures.
Desorption is the release of a substance from or through the surface of a material. In
constant environmental conditions, an adsorbed substance will remain on a surface
almost indenitely. However, as the temperature rises, so does the likelihood of
desorption occurring.
In practical terms, as the temperature of the environment uctuates, water molecules
are adsorbed and desorbed from the internal surfaces of the sample tubing, causing
small uctuations in the measured dew point.
Sample Tubing Length
The sample point should always be as close to the critical measurement point as possible,
in order to obtain a truly representative measurement. The length of the sample line
to the sensor or instrument should be as short as possible. Interconnection points and
valves trap moisture, so using the simplest sampling arrangement possible will reduce
the time it takes for the sample system to dry out when purged with dry gas.
Over a long tubing run, water will inevitably migrate into any line, and the effects of
adsorption and desorption will become more apparent. It is clear from the graph shown
previously that the best materials to resist transpiration are stainless steel and PTFE.
Trapped Moisture
Dead volumes (areas which are not in a direct ow path) in sample lines, hold onto
water molecules which are slowly released into the passing gas; this results in increased
purge and response times, and wetter than expected readings. Hygroscopic materials
in lters, valves (e.g. rubber from pressure regulators) or any other parts of the system
can also trap moisture.

Easidew Plus Portable Hygrometer User’s Manual
10 97478 Issue 1, October 2014
GOOD MEASUREMENT PRACTICE
Sample Conditioning
Sample conditioning is often necessary to avoid exposure of sensitive measuring
components to liquids and other contaminants which may cause damage or affect the
accuracy over time, depending on the measurement technology.
Particulate lters are used for removing dirt, rust, scale and any other solids that may
be in a sample stream. For protection against liquids, a coalescing lter should be used.
The membrane lter is a more expensive but highly effective alternative to a coalescing
lter. It provides protection from liquid droplets, and can even stop ow to the analyzer
completely when a large slug of liquid is encountered.
Condensation and Leaks
Dewpoint > T Dewpoint < T
Maintaining the temperature of the sample system tubing above the dew point of the
sample is vital to prevent condensation. Any condensation invalidates the sampling
process as it changes the water vapor content of the gas being measured. Condensed
liquid can alter the humidity elsewhere by dripping or running to other locations where
it may re-evaporate.
The integrity of all connections is also an important consideration, especially when
sampling low dew points at an elevated pressure. If a small leak occurs in a high
pressure line, gas will leak out but vortices at the leak point and a negative vapor
pressure differential will also allow water vapor to contaminate the ow.

Easidew Plus Portable Hygrometer User’s Manual
Kahn Instruments 11
GOOD MEASUREMENT PRACTICE
Flow Rates
Theoretically ow rate has no direct effect on the measured moisture content, but in
practice it can have unanticipated effects on response speed and accuracy. The optimal
ow rate varies depending on the measurement technology, and can always be found
in the instrument or sensor manual.
An inadequate ow rate can:
• Accentuate adsorption and desorption effects on the gas passing
through the sampling system.
• Allow pockets of wet gas to remain undisturbed in a complex sampling
system, which will then gradually be released into the sample ow.
• Increase the chance of contamination from back diffusion: ambient air
that is wetter than the sample can ow from the exhaust back into the
system. A longer exhaust (sometimes called a pigtail) can also help
alleviate this problem.
• Slow the response of the sensor to changes in moisture content.
An excessively high ow rate can:
• Introduce back pressure, causing slower response times and
unpredictable effects on equipment such as humidity generators.
• Result in a reduction in heating capabilities of the sensor tile during the
initialization period. This is most apparent with gases that have a high
thermal conductivity such as hydrogen and helium.
Which Gases to Measure?
The Easidew Plus Portable Hygrometer is suitable for measurement of the moisture
content of a wide variety of gases. In general, if the gas (in conjunction with water vapor)
is not corrosive to ceramics or base metals then it will be suitable for measurement.
!
POSSIBLE INJURY! The tubing, valves and other apparatus
attached to this instrument must be adequate for the
maximum pressure which will be applied, otherwise physical
injury to the operator or bystander is possible.
!Before disconnecting the Easidew Plus Portable Hygrometer
from the gas line it is essential to vent the system to
atmospheric pressure, otherwise severe injury could result.

Easidew Plus Portable Hygrometer User’s Manual
12 97478 Issue 1, October 2014
MAINTENANCE
5 MAINTENANCE
Routine maintenance of the Easidew Plus Portable Hygrometer is conned to regular
re-calibration of the internal, removable polymer capacitive sensor and replacement of
the lter cartridge.
5.1 Calibration
The calibration of the internal sensor is traceable to national standards. For this reason
it should only be calibrated in an accredited, US National Institute of Standards and
Technology (NIST) standards laboratory. If these facilities do not exist it is recommended
that the sensor returned to Kahn Instruments. A calibration certicate bearing a seven-
point calibration is issued with each sensor.
In most applications, annual re-calibration insures that the stated accuracy of the
Easidew sensor is maintained.
5.2 Sensor / Battery Replacement
To remove the sensor, or battery pack:
1. Insure that the instrument is switched off and that the battery charger,
current output and any sampling components are also disconnected.
2. Remove and retain the 10 Phillips-head screws from the top plate.
3. Lift the small battery pack cover in the top right corner of the instrument.
A small at bladed screwdriver may be required to gently pry the edges
of the cover if it has become stuck to the waterproof seal underneath.
Removing this cover rst will make it easier to lift the entire top panel out
of the instrument.
4. Lift the top plate of the instrument out of the case. Disconnect the battery
pack before removing the top plate completely to prevent it from straining
on the attached cable. If only replacing the battery pack, do not follow
the next two steps.
5. Undo the screw from the center of the sensor connecting plug and pull
off the connector.
6. Unscrew the sensor from the block.
Installing the replacement is simply a reversal of the above procedure. When installing
a new sensor it may be necessary to change the alignment of the GDSN connector (see
next page).

Easidew Plus Portable Hygrometer User’s Manual
Kahn Instruments 13
MAINTENANCE
If the front panel prevents the connector from tting onto the sensor, follow the
instructions below:
• Completely unscrew the cable gland on the GDSN connector to release
the cable tension.
• Remove the locking screw from the back of the connector (retaining the
metal O-ring).
• Remove the connector block using a small screwdriver.
• Rotate the connector block and push it back into the connector housing.
Take care not to trap any wires against the hole for the locking screw.


Easidew Plus Portable Hygrometer User’s Manual
14 97478 Issue 1, October 2014
MAINTENANCE
• Replace the locking screw and cable gland.
5.3 Filter Cartridge Replacement
Unscrew the gas inlet tting to reveal the lter, which can then simply be removed for
checking or replacement.
5.4 Checking the Easidew Plus Portable Hygrometer Electronics Calibration


Supply
4-20 mA
PIN 3
PIN 1
(GND) Screen/Shield
Optional
Figure 4 2-Wire Connection - View Showing Rear of Connector Terminal Block
To verify if the display electronics are within calibration, a 4-20mA current source can
be connected in place of the sensor.
At 4 mA the display should show -60.0°Cdp ±0.5°C (-76.0°Fdp ±0.9°F)
At 20 mA the display should show -76.0°Fdp ±0.9°F (-60.0°Cdp ±0.5°C)
If the displayed values are outside of this range, please contact Kahn Instruments'
Service Department.
5.5 List of Spares
P/N Description
SSF-PF-10PK Pack of 10 particulate lter cartridges
MDM50-BAT Replacement battery pack
MDM50-CHR Replacement battery charger

Easidew Plus Portable Hygrometer User’s Manual
Kahn Instruments 15
MAINTENANCE
5.6 Troubleshooting
Symptom Cause Actions
Display shows “ErrI”
Sensor disconnected or
sensor element / sensor
thermistor fault.
NOTE: This error is
normally displayed
during the rst few
seconds while the
instrument is starting
up.
Check sensor cable is securely
connected inside instrument.
Check instrument electronics with
4-20mA source.
Exchange sensor.
Display shows “ErrL”
Sensor reading under-
range.
Sensor current signal
< 4mA.
Sensor element open
circuit.
Check instrument electronics with
4-20mA source.
Exchange sensor.
Display shows “ErrH”
Sensor reading over-
range.
Sensor current signal >
20mA.
Sensor element short
circuit.
Sensor may have been exposed
to saturation conditions or liquid
contamination. Check that lter and
sensor guard are clean and dry.
If liquid water has contacted sensor,
or sensor block, then disassemble
and dry thoroughly. After drying, it
is recommend to purge assembled
instrument with very dry (-103°Fdp
(-75°Cdp) / 1ppmVmoisture) air for
12 to 24 hours.
Exposure to other contaminants can
cause lasting damage and may require
sensor to be exchanged.
Check instrument electronics with
4-20mA source.
Display ickers on
and off Battery voltage low. Connect charger.
Display off but
battery meter full Battery voltage low. Connect charger.