1

Version

PCS INSTRUMENTS
Fuels and Lubricants Test Equipment

HFRR Humidity
Controlled Cabinet
HFRR Humidity Controlled Cabinet
Revision 1.8

PCS Instruments
78 Stanley Gardens • Acton
LONDON W3 7SZ, UK
Phone +44 (0)20 8600 9920 • Fax +44 (0)20 8600 9921
info@pcs-instruments.com
COPYRIGHT NOTICE

The Copyright in this work is vested in PCS Limited. The document is issued in confidence solely for the
purpose for which it is supplied. Reproduction in whole or in part or for use for tendering or
manufacturing purposes is prohibited except under agreement with or with the written consent of PCS
Limited and then only on the condition that this notice is included in any such reproduction.

ii
I N T R O D U C T I O N

Table of Contents
COPYRIGHT NOTICE ii
Introduction 2
Safety Precautions 3
Installation 4
3.1 Operating Environment 4
3.2 Electricity Supply 5
3.3 Controls 5
3.4 Setting up Procedure 6
3.4.1 Hygrometer installation 7
3.4.2 Controlling the humidity 9

Operation 14
Maintenance 15
Specifications 16

1
 1
Chapter
I N T R O D U C T I O N

Introduction
This Chapter describes the operation of the HFRR
humidity controlled cabinet

The HFRR Humidity Controlled Cabinet (HFRHCAB) is designed as an accessory

for the HFRR High Frequency Reciprocating Rig to allow tests to be carried out at
constant temperature and relative humidity. The cabinet temperature can be
controlled electronically from the prevailing ambient temperature up to 50°C with
stability of ±1°C. The relative humidity within the cabinet can also be controlled
using appropriate salt solutions. Particular combinations of temperature and salt
solution are available which will give an internal absolute vapour pressure of
1.4kPa. This is the “standard” AVP as defined in ISO 12156-1.

Rapid air circulation over the desiccant tray and support platform combined with a
large heat dissipating back plate promotes quick and even heat distribution within
the unit. The plate glass door features a spring-loaded mechanism which maintains
an air-tight seal, ensuring that the internal atmosphere remains constant.

Proven by a third party test house to meet the requirements of the European EMC
Directive, the unit also complies with the safety requirements of the Machinery and
Low Voltage Directives.

The cabinet, which is supplied with a stainless steel stand for the HFRR test head
and a plastic coated desiccant tray, is easy to use and virtually maintenance free.

2
 2
Chapter
S A F E T Y P R E C A U T I O N S

Safety Precautions
This Chapter describes the safety precautions to be
followed when using the humidity cabinet

Beware of hot surfaces and rotating parts.

PCS Instruments cannot be held responsible for any unauthorised modifications to

this unit.

This product and its accessories have been designed and tested to ensure that they
are supplied to you in a safe condition.

These instructions contain information and warnings which you must follow to
keep the equipment in a safe condition, and to ensure safe operation.

If you think that the protection of the equipment may have been impaired for any
reason, for example:-

- It shows visible damage.

- It fails to perform the intended function.

Then the equipment should immediately be returned to PCS Instruments for

investigation and no attempt should be made to operate it.

If the equipment is used in a manner not specified by the manufacturer, then

protection provided by the equipment may be impaired.

3
 3
Chapter
I N S T A L L A T I O N

Installation
This Chapter describes the humidity cabinet installation
procedure.

3.1 Operating Environment

This unit is intended to be used in a residential, commercial, and light
industrial environment as laid down in EN50081-1 and EN50082-1.

This unit is intended for indoor use, under the following environmental
conditions;

Ambient temperature range 5 to 40°C

Altitudes up to 2000m
Ambient relative humidity up to 80% (non-condensing)
Pollution degree 2
Class 1 equipment

The cabinet is supplied ready for connection to an electricity supply, see next
section.

4
I N S T A L L A T I O N

3.2 Electricity Supply

WARNING - This equipment must be earthed.

If for any reason the mains plug has to be replaced, the terminals must be
connected as follows:

(230 or 110 volts 50Hz/60Hz)

Blue wire - Neutral

Brown wire - Live

Green/Yellow wire - Earth

The mains plug should be fitted with a 3A fuse.

3.3 Controls
The control panel is located on top of the cabinet as shown below:

The control panel consists of a temperature control dial that regulates the heating
element inside the cabinet to the desired temperature in Degrees Celsius. The lamp
located beside the temperature control dial is the heating indicator lamp (amber).
This will illuminate amber when the heating element is on. The temperature is
automatically controlled by a thermostat inside the cabinet.

The mains power switch is located to the right of the control panel.

The fuse holder is fitted at the rear of the control compartment. See specifications
section for fuse rating. To remove the fuse from the holder, a flat head screwdriver
is required.

When the mains power switch is illuminated green (on), the internal fan should
rotate to circulate the air inside the cabinet. Please note that on the 110V versions,
the mains power switch does not illuminate.

The temperature scale is calibrated to give an approximate setting of the cabinet

temperature. The final setting should be made with reference to the supplied
hygrometer probe. When the required temperature is set at or near to room
temperature, an initial overshoot can be expected. This error can be reduced by
setting the control knob a few degrees lower than required, and then slowly
increasing this setting until the desired temperature is achieved.

5
I N S T A L L A T I O N

3.4 Setting up Procedure

Shut down the HFRR system if it is already in use. Disconnect the multi-way cable
and the RTD cable from the control unit and the HFRR test head. Keep these
cables in a safe place.

When unpacking the cabinet, the items included are:

 Desiccant tray

 Support platform

 Hygrometer and connecting cable

 Mains Power cable

Position the cabinet next to the control unit. The two cables on the left-hand side
of the cabinet will be pre-set to the correct length, so about 200mm of cable is left
inside the cabinet. If required, each cable can be adjusted by pulling gently to the
desired length.

Circular multi-way cable

RTD connecting cable

Place the support platform within the cabinet with the flat surface uppermost. The
desiccant tray will eventually sit on the cabinet base below the platform, after filling
with the required saturated salt solution.

Position the HFRR mechanical test head on the support platform so that the front
of the test head is about 50 mm from the glass door when it is in the closed
position. Connect the two cables to the rear of the test head and adjust the cable
lengths inside the cabinet (if required) so that the cables are not touching the
stainless steel radiator plate in the rear of the cabinet.

Connect the Main RTD probe to the rear of the HFRR test head to finalise
connections inside the cabinet. Connect both multi-way and RTD connecting
cables from outside the cabinet to the rear of the HFRR control unit.

6
I N S T A L L A T I O N

3.4.1 Hygrometer installation

The humidity and temperature are measured using a hygrometer connected directly
to the rear of the HFRR control unit.

Hygrometer extension cable and

probe supplied with the humidity
cabinet

Connect the probe to the extension cable as follows:

Below shows the pin configuration of the extension cable and probe sockets.

Insert the probe into the extension cable socket and twist to lock both together.

Twist to lock

7
I N S T A L L A T I O N

Connect the extension cable to the socket that is located at rear of the HFRR
control unit as shown below:

Socket for Twist to lock

extension
cable

Insert the probe fully through the humidity cabinet cable gland and tighten gently
as shown below:

Twist to lock

Ensure that the probe is inserted into the cable gland such that the whole of the
end section of the probe (the filter area) is inside the chamber.

ENSURE THIS SECTION IS

INSIDE THE CHAMBER

8
I N S T A L L A T I O N

3.4.2 Controlling the humidity

The humidity is controlled by a mix of solution combining of salt and de-ionised

water that is filled into the desiccant tray inside the cabinet.

The salt is not supplied with the humidity cabinet and will need to be purchased
separately.

The salt solution that we recommend for controlling the humidity inside the
cabinet is either Potassium Carbonate (K2CO3) or Magnesium Nitrate Mg(NO3)2.
Laboratory reagent grade is acceptable.

Magnesium Nitrate can also be found as Magnesium Nitrate Hexahydrate

Mg(NO3)2 · 6H2O.

The optimum laboratory ambient temperature should preferably be 2°C (Degrees

Celsius) below the desired operating temperature inside the cabinet to achieve good
temperature stabilisation. The rate of stabilisation inside the cabinet is determined
by how long the door is opened, coinciding with the change in conditions from
outside the cabinet. The cabinet door should be closed if not in use, as this will
help reduce the stabilisation time required before each test can be started.

The following salt solutions should be chosen with regard to the humidity cabinet
ambient temperature. As the humidity cabinet cannot cool the ambient
temperature, the table below indicates the available salt solutions that have been
known to work inside the cabinet. A suitable operating temperature should be
chosen that works well with the ambient laboratory conditions.

Salt Humidity (%) Humidity (%) Humidity (%) Salt Water

at 20°C at 25°C at 30°C (g) (ml)
Potassium
43 43 43 700 500
Carbonate

Magnesium
54 52 50 1000 180
Nitrate

Please note the table contents are only approximations chosen for the humidity
cabinet and may very slightly depending on mixture.

9
I N S T A L L A T I O N

Potassium Carbonate

The approximate humidity that is created from this salt solution is 43% RH
(relative humidity) up to approximately 30°C (Degrees Celsius).

Items required:

 Beaker, 500ml or greater (preferably an oversized beaker)

 Stirring rod

 Potassium Carbonate (K2CO3), laboratory reagent grade – 700g

 De-ionised water – 500ml

Creating the solution:

When making a saturated solution, take care to observe all precautions appropriate
to the particular chemical. The aim is to create an oversaturated salt solution inside
the cabinet tray.

To make up the saturated solution, you will need 500ml of de-ionised water and at
least 700g of Potassium Carbonate. Start by filling the beaker with 500ml of de-
ionised water and gradually add the salt while mixing. When the salt is mixed with
the de-ionised water the beaker will get slightly warm, so caution must be taken
while handing the beaker.

Not all of the salt will dissolve with the de-ionised water, so when saturation has
been reached inside the beaker, pour the solution slowly into the tray as shown on
the next page. Pull the tray slightly outwards, so as to enable the solution in the
beaker to be poured more easily.

10
I N S T A L L A T I O N

Add the remaining amount of salt into the tray and distribute so it can become
immersed in the de-ionised water as shown below:

Slide the tray back so the front is level with the support platform.

Leave the salt solution to become saturated and then evenly distribute the salt until
there is undissolved solid in the bottom of the tray as shown below:

In order for the humidity control to work properly, there must always be a mixture
of free liquid and undissolved solid in the tray.

It will initially take a couple hours for the salt solution to reach equilibrium with the
air in the cabinet. It is recommended to leave the cabinet door open while the
solution is settling. Switch on the cabinet, so the circulating fan inside is activated
and set the temperature control knob to approximately 25°C.

After the solution has settled, close the cabinet door. Allow both temperature and
humidity to stabilise.

The temperature control will need some fine tuning to get the cabinet temperature
close to 25°C, but with care +/- 0.5°C is achievable. The HFRR test head will also
generate heat inside the cabinet while a test is in operation, so the cabinet
temperature control may have to be lowered to compensate for this extra output in
heat. Optimum lab conditions should preferably be below 23°C for good
temperature stabilisation inside the cabinet.

11
I N S T A L L A T I O N

Magnesium Nitrate

The approximate humidity that is created from this salt solution ranges from 52 to
54% RH (relative humidity), up to approximately 30°C (Degrees Celsius). In regard
to the ISO 12156-1:2016 test method, the desired cabinet operating temperature is
22.5°C.

Items required:

 Beaker, 200ml or greater

 Stirring rod

 Magnesium Nitrate Hexahydrate Mg(NO3)2 · 6H2O, laboratory reagent

grade – 1kg

 De-ionised water – 180ml

Creating the solution:

When making a saturated solution, take care to observe all precautions appropriate
to the particular chemical. The aim is to create an oversaturated salt solution inside
the cabinet tray.

To make up the saturated solution, you will need approximately 180ml of de-
ionised water and 1kg of Magnesium Nitrate. Start by filling the beaker with 180ml
of de-ionised water.

Pull the tray slightly outwards, so as to enable the water in the beaker to be poured
more easily.

12
I N S T A L L A T I O N

Gradually pour the salt into the tray and mix. The Magnesium Nitrate should
dissolve quickly into the tray.

Slide the tray back, so the front is level with the support platform.

In order for the humidity control to work properly, there must always be a mixture
of free liquid and undissolved solid in the tray.

It will initially take a while for the salt solution to reach equilibrium with the air in
the cabinet. Switch on the cabinet, so the circulating fan inside is activated and set
the temperature control knob to approximately 22°C.

After the solution has settled, close the cabinet door. Allow both temperature and
humidity to stabilise.

The temperature control will need some fine tuning to get the cabinet temperature
close to 22°C, but with care +/- 0.5°C is achievable. The HFRR test head will also
generate heat inside the cabinet while a test is in operation, so the cabinet
temperature control may have to be lowered to compensate for this extra output in
heat. Optimum laboratory conditions should preferably be below 20°C for good
temperature stabilisation inside the cabinet.

Additional Factors

The position of the cabinet must also be considered, so placing the cabinet near to
a direct source of heat output e.g. near a window with sunlight exposure, can affect
the temperature inside the cabinet.

Once the temperature and humidity have stabilised, check the solution in the
desiccant tray to make sure it is still correctly saturated. Add more salt or de-
ionised water if necessary.

Keep a stirring rod available inside the cabinet as this will be required to
periodically mix the solution if the humidity correction does not respond as quickly
as desired when the door is closed.

13
 4
Chapter
O P E R A T I O N

Operation
This Chapter describes the humidity cabinet operation.

Operation of the HFRR system with the humidity cabinet is the same as before.

Prepare the specimens and have them ready to fit onto the test head before
opening the cabinet door. Keep the cabinet door open for the minimum time
possible, as this will reduce the time taken for the environment to re-equilibrate
before the test is started. The time taken for the temperature and humidity to re-
equilibrate after the specimens have been loaded and the door has been closed
depends on the difference between the conditions inside and outside the cabinet.

In most operating environments the ambient humidity outside the cabinet will be
lower than that inside so that dry air will be introduced to the cabinet when the
door is opened. This will result in the gradual loss of water from the saturated salt
solution. It is recommended to keep a small bottle of de-ionised water inside the
front of the cabinet (so that it is at the correct temperature) to replenish the
saturated solution as necessary. Take care not to add too much water in case all of
the solid salt dissolves. In high ambient humidity environments, water will
condense into the saturated solution allowing more salt to dissolve. In this case it is
necessary to periodically remove some of the saturated solution and add more dry
salt.

In order for the humidity control to work properly, there must always be a mixture of free solution
and undissolved solid in the desiccant tray.

14
 5
Chapter
M A I N T E N A N C E

Maintenance
This Chapter describes the humidity cabinet maintenance
required.

There are no user serviceable parts on the cabinet.

Keep the interior of the cabinet clean and dry. Be especially careful to wipe up
spills of fuels/lubricants and of water or salt solution.

Periodically clean the door seal so that it makes good contact with the glass door.

Should the salt solution become contaminated with fuels/lubricants or other

substances it will have to be replaced. Over time it is also likely that the solution
will pick up dust and dirt from the air and again it should be replaced if this is a
problem.

15
 6
Chapter
S P E C I F I C A T I O N S

Specifications
This Chapter lists the humidity cabinet specifications

SIZE (Dimensions in mm)

External (overall): 640 x 390 x 630

Internal: 530 x 350 x 500
Door aperture: 425 x 325

CONSTRUCTION

Cabinet: Stainless steel

Fittings : Plated/Painted steel
Door: Plate glass

FINISH

Interior: Stainless steel

Exterior: Powder coated

POWER SUPPLY

Voltage: 230VAC or 100/110VAC 50/60Hz

Power: 120 VA
Fuse (cabinet): 1A (230VAC) or 2.5A (100/110VAC)
Fuse (mains plug): 3A

WEIGHT

Net: 17 Kg

All figures are approximate and exclude protrusions.

16