Sullair SD-820 Series User manual

SD Heatless Desiccant Compressed Air Dryer
User Manual
For Model Series SD-820 to -1710
With Dewpoint Dependent Switching
This dryer includes equipment
options as selected (X) below:
DDS OPTION
EDP OPTION
3V OPTION
This Manual is part number 02250159-760
Applicable for dryers serial number 13982 and up
Revision 04, October 2005

II

USER MANUAL
Models SD-820 to SD-1710 with DDS
Rev 04 – October 2005
III
FOREWORD
Reading this user manual will fully familiarize you with the Sullair adsorption dryer. You
will be better able to run this equipment in accordance with its intended use.
This manual contains important information for safe, proper and economic dryer
installation, start-up, operation and maintenance. Always keep it within reach where the
adsorption dryer is being used.
It is necessary to follow all instructions as written. Careful reading will avert danger,
avoid unnecessary downtime, and minimize work for yourself and wear on the
equipment.
In addition to carefully reading this technical manual in its entirety, you must understand
your National, State and local rules and regulations regarding safety in the workplace,
their necessary precautions and procedures.
Each person responsible for the set-up, start-up, operation, maintenance or repair of
this adsorption dryer must have first read and understood this user manual – including
all the safety tips.
NOTE: Sullair recommends that installation, start-up and maintenance be carried
out by its factory-trained technicians in a regularly scheduled, site-
dedicated program. This will ensure the safety of personnel, the integrity
of equipment and the surety of warranty coverage.

USER MANUAL
Models SD-820 to SD-1710 with DDS
Rev 04 – October 2005
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USER MANUAL
Models SD-820 to SD-1710 with DDS
Rev 04 – October 2005
v
TABLE OF CONTENTS
1. INTRODUCTION...........................................................................................................................................1
1.1 GENERAL.....................................................................................................................................................1
1.2 PRODUCT INFORMATION ...............................................................................................................................1
1.2.1 Pressure Vessel Regulations..................................................................................................................2
1.2.2 Leak Test...............................................................................................................................................2
1.3 SAFETY INSTRUCTIONS.................................................................................................................................2
1.3.1 Identification of Signs and Symbols in this Manual.................................................................................2
1.3.2 General Safety Tips for Assembly, Inspection and Maintenance..............................................................3
1.4 TECHNICAL DATA SHEET..............................................................................................................................4
1.5 OVERLOADING .............................................................................................................................................5
1.6 TRANSPORT..................................................................................................................................................5
1.7 STORAGE .....................................................................................................................................................5
1.8 USE OF A PREFILTER AND AFTERFILTER ........................................................................................................5
2. INSTALLATION............................................................................................................................................7
2.1 GENERAL.....................................................................................................................................................7
2.2 ELECTRICAL CONNECTION............................................................................................................................7
2.3 FILTERS .......................................................................................................................................................7
2.4 PURGE EXHAUST..........................................................................................................................................8
2.5 DDS CONTROL CONNECTION........................................................................................................................8
3. EQUIPMENT OPERATION ..........................................................................................................................9
3.1 GENERAL OPERATING PRINCIPLES ................................................................................................................9
3.2 OPERATORCONTROLS ................................................................................................................................10
3.3 INITIAL START-UP......................................................................................................................................12
3.4 SHORT-TERM SHUT-DOWN.........................................................................................................................13
3.5 SHUT-DOWN IN CASE OF A FAULT OR FOR MAINTENANCE ........................................................................... 13
3.6 RESTARTING ..............................................................................................................................................13
3.7 ALARMS.....................................................................................................................................................14
3.7.1 Hygrometer Failure Alarm ..................................................................................................................14
3.7.2 High Humidity Alarm..........................................................................................................................14
3.7.3 Common Alarm Relay..........................................................................................................................14
4. MAINTENANCE........................................................................................................................................... 15
4.1 CHECKLIST.................................................................................................................................................15
4.1.1 Daily Check ........................................................................................................................................ 15
4.1.2 Weekly Check......................................................................................................................................15
4.1.3 Whichever Is First: After Each 2,500 Operating Hours or Annually ....................................................16
4.2 CHANGING THE FILTER ELEMENT................................................................................................................ 16
4.3 REPLACEMENT OF THE DESICCANT..............................................................................................................17
4.4 CHANGING THE PURGE REGENERATION ORIFICE.........................................................................................18
5. SPARE PARTS LIST....................................................................................................................................19
5.1 SD-820 TOSD-1050...................................................................................................................................19
5.2 SD-1200 TOSD-1710.................................................................................................................................20
6. FAULTS AND TROUBLESHOOTING .......................................................................................................21
6.1 DEW POINT TOO HIGH ................................................................................................................................21
6.2 TOWERS DONOT SWITCH OVER .................................................................................................................21
6.3 BACK PRESSURE TOO HIGH DURING REGENERATION................................................................................... 22
7. DRAWINGS..................................................................................................................................................23

USER MANUAL
Models SD-820 to SD-1710 with DDS
Rev 04 – October 2005
vi
APPENDIX A– DRYER OPERATING SEQUENCE....................................................................................A-1
APPENDIX B – DRYER FLOW CAPACITY.................................................................................................B-1

USER MANUAL
Models SD-820 to SD-1710 with DDS
Rev 04 – October 2005
1
1. INTRODUCTION
1.1 GENERAL
This dryer includes the latest technology and safety features. Its use, however, can
endanger life and limb and can lead to considerable damage to the equipment and
other material assets if:
 it is operated by personnel not instructed in its use,
 it is improperly used,
 it is improperly maintained or serviced.
Furthermore, ignorance of its use and maintenance can result in the loss of any claim
for damage.
This adsorption dryer is designed for neutral media (such as air or nitrogen) which is
free of aggressive water, oil and solid elements. Sullair accepts no liability for corrosion
damage or malfunctions caused by aggressive media.
Applications other than those mentioned in this manual must be agreed to by Sullair and
confirmed in writing.
This dryer additionally requires the installation of Sullair pre- and afterfilters (refer to
paragraph 1.8) which are shipped separately.
Sullair reserves the right to make changes at any time as may be necessary for
increasing safety or efficiency, or in the interests of further product development.
1.2 PRODUCT INFORMATION
The adsorption dryer is used for the purpose of drying compressed air and other gases
according to its contracted design. Depending on certain conditions at the inlet, and
with pre- and afterfilters properly installed, it provides pure, dry and oil-free compressed
air or gases. The standard model of adsorption dryer is equipped with two desiccant
vessels.
This specific model of dryer includes a Dewpoint Dependent Switching (DDS) system
that provides automatic monitoring and control of the work/regeneration cycle to
optimize equipment efficiency. This manual also includes references to optionally
available Enhanced Dew Point (EDP) and 3-Valve Bypass (3V) systems/assemblies
which may or may not be provided. Selected options included with this dryer are
indicated on the cover page by an “X” mark in the box.

USER MANUAL
Models SD-820 to SD-1710 with DDS
Rev 04 – October 2005
2
1.2.1 PRESSURE VESSEL REGULATIONS
The pressure vessels are designed and built to meet the American Society of
Mechanical Engineers (ASME) standards. They fulfill the test of the certifying procedure
and carry the ASME symbols Uor UM.
RANGE OF APPLICATION
Design Pressure Max: 150 psig
Design Temperature Max: 500 °F (260 °C)
Min: -20 °F (-29 °C)
1.2.2 LEAK TEST
Each Sullair adsorption dryer is subjected to, and must pass, a leak test prior to
shipment.
1.3 SAFETY INSTRUCTIONS
This manual contains basic tips which must be followed during set-up, operation and
servicing. It is of utmost importance that it be read by the assembly technician before
installation and start-up as well as by the specialist/operator in charge. It must always
be within reach at the place where the adsorption dryer is being used.
1.3.1 IDENTIFICATION OF SIGNS AND SYMBOLS IN THIS MANUAL
The safety tips contained in this manual, whose disregard could endanger people and
equipment, are indicated by a general danger sign and the additional markings Danger!
or Attention! or Warning!
Danger! / Attention!
Safety sign in accordance with DIN 4844 - W9
Warning – high voltage!
Safety sign in accordance with DIN 4844 - W8
Safety tips printed directly on the adsorption dryer must be heeded at all times and must
be kept completely legible.

USER MANUAL
Models SD-820 to SD-1710 with DDS
Rev 04 – October 2005
3
1.3.2 GENERAL SAFETY TIPS FOR ASSEMBLY, INSPECTION AND MAINTENANCE
The purchaser is to ensure that all assembly, maintenance and inspection work is
carried out by personnel qualified to do it.
The personnel involved in assembly, operation, maintenance and inspection must have
the corresponding qualifications to do this work. Areas of responsibility and supervision
of the personnel must be clearly established by the purchaser. Should the personnel
not possess the necessary knowledge, then they must be instructed. If need be, this
training may be carried out by the manufacturer/supplier at the request of the purchaser.
Further, the purchaser is to ensure that all personnel completely understand and follow
the content of this manual.
Attention!
Never make structural changes to the adsorption dryer
Only use recommended spare parts as listed in section 5
Never weld on a pressure vessel or change it in any way
Carry out maintenance only when the adsorption dryer is OFF,
depressurized and disconnected from the electric power supply.
Danger!
Wear protective clothing and goggles when working with the
desiccant
If desiccant comes into contact with the eyes, rinse eyes
immediately with a lot of clear water
If the desiccant is spilled, clean up without causing swirls of dust
In case of fire, there is no restriction on the use of fire extinguishing
material on the desiccant; the reaction with water and foam is
defined as strong
A mask must be worn whenever handling desiccant.

USER MANUAL
Models SD-820 to SD-1710 with DDS
Rev 04 – October 2005
4
1.4 TECHNICAL DATA SHEET
All values given in the table below assume a standard dryer with a standard scope of
supply and standard operating conditions.
SD-820 SD-1050 SD-1200 SD-1450 SD-1710
Process medium Air, free of aggressive elements
Flange (150#) connections
(inches) 33333
Flow capacity (1) (SCFM) 820 1050 1200 1450 1710
Flow capacity with EDP
option (2) (SCFM) 574 735 840 1015 1197
Desiccant Activated alumina
Qty of desiccant per
chamber (pounds) 460 600 700 800 952
Recommended filter size
(SCH/SCR) 910 1315 1315 2120 2120
Controls Printed Circuit Board
Operating electrical power 110, 115, 120 Vac / 1 Phase / 50, 60 Hertz
Drying time per tower Standard: 5 minutes
With EDP Option: 2 minutes (2)
DDS activation setting Standard: -41.8oF (-41oC)
With EDP Option: -101oF (-74oC) (2)
High humidity alarm setting Standard: -32.8oF (-36oC)
With EDP Option: -96oF (-69oC) (2)
(1) NOTE: At standard inlet conditions of 100oF, 100 psig, and providing a –40oF pressure dew point
according to DIN ISO 7183.
(2) NOTE: EDP Option indicates a dryer which has been specifically set up at the factory to obtain a
pressure dewpoint of -100oF. Paragraph 1.2 identifies the options provided with this dryer.
This option requires reduction of the rated flow. Contact Sullair for details.

USER MANUAL
Models SD-820 to SD-1710 with DDS
Rev 04 – October 2005
5
1.5 OVERLOADING
Attention!
Protect the adsorption dryer from overloading!
The adsorption dryer can become overloaded if:
The flow volume of the medium to be dried increases
The temperature of the air at entry and, correspondingly, its
humidity increases
The minimum operating pressure decreases
The prefiltration and separation of impurities are not sufficient or the
filter drain fails
Introduction of oil into the air stream.
1.6 TRANSPORT
Immediately upon delivery of the dryer, it must be checked for any damage that may
have occurred during transport. If necessary, the damage must be recorded on the
shipping waybill/receipt. Liability for such damage usually rests with the shipper.
Contact Sullair to arrange for any required service or replacement parts.
Attention!
For transport within your company site, only the skid of the adsorption
dryer may be used for lifting. Lifting at any other points on the equipment
will void the warranty and damage the equipment.
1.7 STORAGE
If the adsorption dryer is to be stored for a long period of time, its place of storage must
be dry and free of dust. The ambient temperature must not go below 33°F (+1°C).
1.8 USE OF A PREFILTER AND AFTERFILTER
In order to prevent droplets of condensate, oil and dirt from getting into the desiccant, a
Sullair SCH 0.01-micron coalescing prefilter with an automatic condensate drain must
be installed upstream of the adsorption dryer. Otherwise an oil film on the desiccant
would reduce the drying capacity and adversely affect performance.
In order to prevent breakdown in downstream consumers caused by material that has
been abraded from the desiccant bed, a Sullair SCR 1-micron particulate afterfilter must
be mounted downstream of the adsorption dryer. Since no condensate accumulates in
the afterfilter, this filter is normally equipped with a manual vent valve.

USER MANUAL
Models SD-820 to SD-1710 with DDS
Rev 04 – October 2005
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1.8 USE OF A PREFILTER AND AFTERFILTER (CONTINUED)
Both filters should be equipped with an incident monitor (i.e., differential pressure
indicator) to advise of premature blockage of the filter elements. Elements must be
changed annually regardless of the reading on the indicator.

USER MANUAL
Models SD-820 to SD-1710 with DDS
Rev 04 – October 2005
7
2. INSTALLATION
2.1 GENERAL
Ensure that the installation site is free of dust, dirt and litter. The site floor must be level
and strong enough to support the equipment. The site itself must ensure that the
equipment will not, under any circumstances, experience ambient temperatures below
freezing.
Ensure that the Sullair dryer is carried only by its skid base frame. It must be positioned
so that the side from which it is to be operated is easily accessible. The piping is to be
connected at a slightly downward slope toward the prefilter. Install isolation valves on
the inlet and outlet sides of the dryer. Also, a bypass pipe with an additional valve
should be mounted around the dryer to allow for an uninterrupted supply of compressed
air when it requires maintenance or repair. The bypass assembly is optionally provided
(see paragraph 1.2) or can be customer furnished. If vibration occurs at the installation
site, the adsorption dryer skid frame must be placed onto vibration dampers.
2.2 ELECTRICAL CONNECTION
Since the adsorption dryer has already been completely wired at the factory, the
customer only has to connect the power supply cable to the terminal strip according to
the supplied wiring diagrams (see section 7).
Warning – high voltage!
Be sure that power is removed from the line feed before making
connection between the site drop and the equipment.
This Sullair adsorption dryer is normally controlled with a printed circuit board. The set
times are adjusted at the factory during the test run. Do not change these
adjustments!
NOTE: Contact Sullair if you have any questions.
2.3 FILTERS
If not already factory installed, you must install a 0.01-micron coalescing (SCH) prefiliter
with an automatic condensate drain upstream of the desiccant dryer and 1 micron
particulate (SCR) afterfilter with manual vent valve downstream of the desiccant dryer.
Refer to the filter manual for proper installation.

USER MANUAL
Models SD-820 to SD-1710 with DDS
Rev 04 – October 2005
8
2.4 PURGE EXHAUST
The purge exhaust may be piped to an open vent. Noise levels at the dryer may be
reduced by extending the purge exhaust piping to a remote location. Refer to the purge
piping selection chart below to prevent excessive backpressure which may adversely
affect dryer performance.
EXTENDED LENGTH PIPE SIZE REQUIRED
TO 10 FEET SAME SIZE AS DRYER EXHAUST
TO 25 FEET 1 SIZE LARGER THAN DRYER EXHAUST
TO 50 FEET 2 SIZES LARGER THAN DRYER EXHAUST
TO 100 FEET 3 SIZES LARGER THAN DRYER EXHAUST
Extending purge exhaust piping must not cause excessive back pressure on the
chamber being regenerated. A pressure reading of 3-psig there is considered too high
for the dryer to regenerate efficiently.
2.5 DDS CONTROL CONNECTION
Check that the sample line (1/8-in Teflon tube) is connected from the dryer outlet (see
flow schematic in section 7) to the inlet valve on the humidity probe sample cell. The
humidity probe comes in a transport container found inside the control panel. Remove
probe from container and install it in the sample humidity cell (see figure 1). Close the
container and keep it inside the control panel for future maintenance.
Connect the coaxial cable to the humidity probe.
FIGURE 1 – HUMIDITY CELL ASSEMBLY

USER MANUAL
Models SD-820 to SD-1710 with DDS
Rev 04 – October 2005
9
3. EQUIPMENT OPERATION
3.1 GENERAL OPERATING PRINCIPLES
This Sullair dryer has two parallel adsorption chambers filled with desiccant. While the
medium is being dried flowing bottom-up in one chamber, regeneration takes place from
the top down in the other chamber. The changeover from one chamber to the other is
controlled by the Dewpoint Dependent Switching system that monitors desiccant
performance by measuring the outlet air dew point. It operates continuously and is fully
automatic.
The standard dryer with DDS has a cycle time of 10 minutes. Dryers with the Enhanced
Dew Point option have a 4-minute cycle time. In each case, half the cycle time is
dedicated to air drying and the other half to desiccant regeneration, with one chamber
working to dry the air while the other regenerates. The cycle time affects air flow and air
quality. The longer cycle time allows greater saturation of the desiccant, thereby
decreasing its drying capacity over the period of the cycle. The faster cycling provided
with the EDP option ensures that the desiccant is regenerated more frequently, thereby
enhancing its drying performance. The dryer is configured at the factory. The principles
of operation are the same for both the standard (with DDS) and the EDP dryers.
Wet air enters the working desiccant chamber (it can be either the left or right) at the
inlet switching valve (bottom) and is dried as it flows upward through the desiccant bed.
Dry air exits the dryer through the outlet check valve.
At the outlet of the working chamber, a portion of the dry air (i.e., purge air) is diverted
to the regenerating chamber. That purge air, at near atmospheric pressure, will remove
previously adsorbed moisture as it flows downward through the desiccant bed and exits
through the purge exhaust muffler.
The purge air is controlled by a purge adjusting valve and purge orifices located in the
purge line. Purge pressure is indicated on the purge pressure gauge. Refer to
Appendix B for instructions on adjusting the purge rate.
Near the end of each half cycle, the chamber being regenerated will be repressurized.
For this to occur, the exhaust valve of the chamber being regenerated closes while
purge air continues to flow. Repressurizing the regenerated chamber to operating
pressure before placing it into service minimizes fluidization of the desiccant and helps
prevent desiccant abrasion which causes desiccant dust to prematurely block pilot filter
and afterfilter elements.
Chamber switchover takes place when both towers are fully pressurized. This
minimizes desiccant movement which, in turn, minimizes creation of dust.
When switchover is complete, the regenerated tower will be placed into service and the
exhausted tower will begin a depressurization/regeneration cycle.

USER MANUAL
Models SD-820 to SD-1710 with DDS
Rev 04 – October 2005
10
When sized correctly, the Sullair type SD air dryer with DDS is designed to provide a
specific pressure dewpoint performance (generally -40°F (-40°C)) at worst-case
operating conditions (maximum flow at lowest pressure and highest inlet temperature).
The regeneration purge flow rate required for the dryer is adjusted to achieve that
dewpoint based on those conditions.
For example, for dryers operating at 100 psig (690 kPa) and 100°F (38°C), the purge
flow rate is approximately 15% of the specified maximum inlet flow. Dryers operating
under less severe inlet conditions will introduce a reduced humidity load. The DDS
controls have been factory programmed to monitor the dryer outlet dewpoint so that
regeneration will only begin when low desiccant performance registers.
Sullair SCH high-efficiency prefilters and SCR reverse-flow afterfilters are designed to
remove solids, oil and water condensate from compressed air and other neutral,
compressed gases. These filters provide high flows and low differential pressures.
Solids are filtered out by impact or by the effect of inertia, whereas oil particles and
drops of moisture are filtered out by the effect of coalescence. Contaminants collect in
the bottom of the filter vessel and are drained either automatically or manually.
Filters are provided separately unless the 3-Valve Bypass option has been purchased
(see paragraph 1.2).
3.2 OPERATOR CONTROLS
This adsorption dryer includes a Dewpoint Dependent Switching system that monitors
the dryer outlet dewpoint performance to set the optimum chamber changeover cycle
for desiccant regeneration.
The operator electrical control panel features the following indicators/controls:
 Dryer nameplate – the nameplate information identifies your dryer
 Three-way selector switch on the left side of the operator control panel:
oDRYER OFF
oDRYER ON
oDDS ON.
 Digital operations status display (see figure 2) used for system monitoring:
oECONOMY CYCLE light emitting diode (LED) – lit when DDS is on

USER MANUAL
Models SD-820 to SD-1710 with DDS
Rev 04 – October 2005
11
3.2 OPERATOR CONTROLS (CONTINUED)
oDEW POINT liquid crystal display (LCD) – shows the currently measured dew
point. The display flashes +20 when the measured dew point exceeds the
factory-set alarm limit.
oPOWER LED– lit when the dryer is powered
oFlow direction LEDs – identify which dryer chamber is drying or regenerating.
The LED lit at an up arrow shows that chamber is drying. The LED lit at a
down arrow indicates that the chamber is in regeneration mode. A chamber
which is finished regenerating, and is standing by, will have no LED lit.
FIGURE 2 – STATUS DISPLAY
There are two Sullair filter assemblies also required for proper dryer operation. The
prefilter housing has an incident monitor (also known as differential pressure indicator)
and an automatic drain. The afterfilter housing has an incident monitor and manual vent
valve.
Each desiccant chamber has a thermal pressure relief valve at the top (for pressure
relief due to thermal expansion in a shut-in condition), a pressure gauge and desiccant
fill/drain (top/bottom) ports.

USER MANUAL
Models SD-820 to SD-1710 with DDS
Rev 04 – October 2005
12
3.3 INITIAL START-UP
Attention!
All pipes and wire connections must be tightened!
Furthermore, before start-up:
 The pipes must be cleaned of scale,abraded material from the
threading, or other similar impurities.
 All isolation valves upstream of the prefilter and downstream of the
afterfilter should be closed. The bypass valve (if installed) should be
open.
 The ambient temperature must not be less than 33°F.
NOTE: Failure resulting from faulty installation or start-up does not fall under the
Sullair warranty obligation. Start-up by factory trained personnel is highly
recommended.
Perform the following tasks in sequence for the initial start-up:
 Remove purge exhaust mufflers for the initial 1 to 2 hours of operation
 Slowly open the inlet isolation valve and observe the pressure build-up on the
chamber pressure gauge of the adsorption dryer. Avoid an abrupt pressure build-
up as this may damage the dryer.
 Turn the switch to the DRYER ON position.
NOTE: Do not switch to DDS ON during the first eight hours of operation.
 The adsorption dryer must be powered approximately 3 to 4 hours with the
isolation valve downstream of the afterfilter closed. This regenerates the
desiccant.
 After the regeneration phase, open the shut-off valve behind the afterfilter slowly
while observing the chamber pressure gauge. If the shut-off valve is opened
abruptly, it could put a stress on the system. Close the bypass valve (if installed).
The adsorption dryer is now ready for operation and functions continuously and fully
automatically. After eight hours of operation, it is appropriate to engage the DDS
feature:
 Fully open the inlet valve to the sample cell
 Partially open the discharge valve of the sample cell to bleed off a small amount
of sample air. Do not fully open discharge valve.

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Models SD-820 to SD-1710 with DDS
Rev 04 – October 2005
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 Perform a soap bubble test to check for leaks on all parts of the sample line,
connections and the humidity sample cell.
 The digital display will read the dew point of the dryer system. It will take a
period of time for a humidity probe to be purged of humidity and read the correct
dew point.
NOTE: The dryer should be operated in the DRYER ON position at the time of
initial start-up and at all times when the hygrometer or humidity probe are
removed for service.
3.4 SHORT-TERM SHUT-DOWN
Follow this sequence when switching off the adsorption dryer:
 First close all the isolation valves up- and downstream of dryer
 Then immediately switch DRYER OFF.
Danger!
Dryer will remain pressurized.
3.5 SHUT-DOWN IN CASE OF A FAULT OR FOR MAINTENANCE
Follow this sequence when switching off the adsorption dryer:
 First close all the isolation valves up- and downstream of the adsorption dryer,
 Depressurize the dryer by using the manual vent valve at the bottom of the
afterfilter,
 Then immediately switch DRYER OFF.
Danger!
Before any kind of maintenance or repair work is done, the dryer must
be depressurized and disconnected from the power source.
3.6 RESTARTING
 Close the manual vent valve at the bottom of the afterfilter
 Slowly open the inlet isolation valve and pressurize the adsorption dryer up to the
regular operating pressure by keeping the isolation valve mounted downstream
of the afterfilter closed.
 Switch DRYER ON.

USER MANUAL
Models SD-820 to SD-1710 with DDS
Rev 04 – October 2005
14
NOTE: If the dryer is restarted after a long standstill, proceed as for an initial
start-up (see paragraph 3.3).
3.7 ALARMS
3.7.1 HYGROMETER FAILURE ALARM
If the hygrometer probe fails, then a fault will be triggered by the hygrometer. The DEW
POINT display on the operator control panel will read 999.
If the hygrometer itself fails or loses power, the DEW POINT display will read either
sens or -999.
3.7.2 HIGH HUMIDITY ALARM
The hygrometer has been programmed to initiate an alarm if the dryer outlet dew point
rises above the setting shown in section 1.4. The DEW POINT display on the operator
control panel will read +20.
3.7.3 COMMON ALARM RELAY
If any alarms are activated, the common alarm relay will also be activated. The alarm
relay does not convey the nature of the alarm, it only provides an output that an alarm
has occurred. The alarm relay is usually connected by the purchaser to a remote
monitoring station.