MICHELL MDM25 Handheld Hygrometer User Manual

MDM25
Hygrometer
User Manual

97234 Issue 4.1
February 2022

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MDM25

For Michell Instruments’ contact information please go to www.michell.com

© 2022 Michell Instruments
This document is the property of Michell Instruments Ltd and may not be copied or otherwise reproduced, communicated in any way to third parties, nor stored in any Data
Processing System without the express written authorization of Michell Instruments Ltd.

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 ensure 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 competent personnel using 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.
Pressure Safety
This product is not suitable for use at pressures greater than atmospheric.
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.michell.com for details of Michell Instruments’ worldwide office’s contact information.
Calibration
Annual calibration is recommended for the RH probe. This should be returned to the manufacturer, Michell Instruments, or one of their accredited service agents for re-calibration.
Safety Conformity
This product meets the essential protection requirements of the relevant EU and UK directives.

Abbreviations

The following abbreviations are used in this manual:

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.

INTRODUCTION

The MDM25 is a battery-operated hand meter.
Available with a number of different probe configurations and the ability to display relative humidity, temperature, absolute humidity (g/m3), dew point, and wet bulb temperature, the MDM25 is suitable for spot-checking humidity in a wide variety of applications.
The hygrometer is contained within a molded ABS housing with a rubber surround for drop protection – sealed to IP54 standards. The rubber surround allows for comfortable
hand-held operation and safe transportation of the unit.
It is powered by 3 alkalines ‘AA’ size cells, which are designed to last a minimum of 150 continuous hours between replacements. Continuous battery charge status indication is
provided by a battery indicator icon.
A graphical display presents the RH and temperature readings, in addition to a selectable third value, in large format characters.

1.1 Description
1.1.1 Controls and Indicators
The controls and indicators associated with the MDM25 hygrometer are located on the front panel.
The probe connection to the MDM25 hygrometer is made to the top panel and The battery charger cover is located on the rear of the instrument.
Figure 1 shows the layout of the controls.

1.1.2 Instrument Display

1| Battery Charge Indicator Icon – displays 3 dots when full. When the battery icon is empty, replace the batteries.
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2| RH Display
3| Temperature Display
4| 3rd Output Display – presents the selected 3rd
output, either in ºC / ºF Td, g/m, or ºC / ºF TW
Battery Indicator

Full battery power|
2/3 battery power|
1/3 battery power|
Replace batteries|

Figure 2 Display

1.2 Display Units
The MDM25 measures relative humidity and temperature. The third output, when displayed, is calculated from these two parameters.
The table below gives a description of all available units.

water vapor pressure (the maximum amount of water vapor that can exist at a given temperature) over a liquid water surface, is expressed as a percentage.
Temperature| Ta| 0C or °F| The temperature of gas determines the maximum quantity of moisture that can be present as vapor in that gas.
Dew Point| Td| 0C or °F| The temperature at which dew, or
condensation, forms, on cooling a gas. This is, therefore, the temperature at which air becomes saturated in equilibrium with the water.
Absolute Humidity| Abs H| g/m3| The mass of water vapor is present in a unit volume of the moist air of a given temperature and pressure. SI (metric) units are grams of water per cubic meter of air (g/m3).
Wet Bulb temperature| Two| 0C or °F| The temperature is indicated by a thermometer sheathed in wet wicking and influenced by the rate of evaporation from the wicking.

Table 1 Unit Descriptions

1.3 Display Settings
The Display Settings Menu contains options to change the contrast ratio, backlight intensity, and orientation of the display.
1.4 Device Settings
The Device Settings Menu contains options to change the period of time before power off, temperature units, and  3rdvalue units.
1.5 About
The About menu gives information about the firmware version and the serial number of the hygrometer.

INSTALLATION

2.1 Unpacking the Instrument
Open the box carefully and unpack the contents. Check that the following items are included. Report any shortages immediately.

• MDM25 Hygrometer
• 3 off Alkaline ‘AA’ cells
• User Manual
• RH & Temp Probe (options available)
• Calibration certificate (optional)

2.2 MDM25 Accessories
Filters and Protection Caps

Probes

• Fixed probe
• Standard probe
• Sword type probe
• Remote high-temperature probe, 300mm (18”)
• Remote high-temperature probe, 500mm (19.6”)

Other

• Carrying case
• Batteries (3 ‘AA’ Alkaline cells)
• Control Kit of calibration salts

2.3 Battery Requirements
The MDM25 is supplied with 3 Alkaline AA-size cells. These non-rechargeable Alkaline cells have a high energy density and long shelf-life.

Do not mix different types of batteries. All three batteries must be of the same type.

2.3.1 Fitting the Batteries
Unscrew the battery compartment and insert the three ‘AA’ cells, according to the image on the inside of the battery compartment.
Refit the compartment cover ensuring the seal is fully compressed.

2.4 Mounting and Connecting the Probe
All probes insert directly into the connector on the top of the MDM25.
Align the locating peg with the locating notch and then rotate the knurled thumbwheel until the probe is securely held in place.

WARNING: Do not over-tighten as this could cause damage to the probe body.

OPERATION

3.1 Preparation for Operation
Press the power-on button and observe the readings on the LCD. Some 3rd values may take a few seconds to calculate, depending upon the %RH and ambient temperature (Ta).
If using the MDM25 alongside the S503 RH calibrator, adjust the display orientation to allow for the product to be read correctly when upside down.
If there is no reading on the screen check the battery orientation. Replace with new batteries if required.

3.2 Overall Menu Structure

3.2.1 Display Settings

To store these settings in the memory, press the Menu button which will open the main page. When the hand meter is turned on again this setting is saved.
To store the settings for ONLY the current session, press the Left Key Figure 6 Display Settings Menu

3.2.2 Device Settings

To store these settings in the memory, press the Menu button to return to the main page. When the hand meter is turned on again this setting is saved. To store the settings for ONLY the current session, press the Left Key Figure 7 Device Settings Menu

3.2.3 About

Press the Menu button to return to the main page.  Figure 8About Menu

MAINTENANCE

The MDM25 is designed to operate either in static ambient conditions or in a flowing gas stream.
The sensors are designed to have excellent performance in ambient conditions.
Therefore, a flow is not necessary to ensure that the probe is reacting rapidly to changes in measured conditions. If the sensor is installed in a flowing sample, then it is not crucial to regulate the flow rate in order to ensure consistent performance, although it is preferable to avoid excessive flow rates past the sensor during operation.
The use of appropriate filtering for the sample conditions is always recommended – so, where the sample or ambient conditions may contain dust, steam or liquid water, a suitable mesh or sintered filter should be fitted. Protection caps are also available to defend against the possibility of handling damage.
Care should be taken to avoid mechanical shock (impact) or thermal shock (sudden temperature changes).

4.1 Probe Calibration
Salt solutions are commonly used for the calibration of RH sensors. Michell Instruments calibration Control Kit is available to provide a traceable reference to verify the accuracy of the probe. The Control Kit can be purchased from Michell Instruments (for contact information go to www.michell.com).
4.2 Cleaning
The enclosure can be cleaned using a mild household detergent and a damp soft cloth or absorbent paper. Remove the connector before cleaning and dry off any moisture before reassembly. NOTE: Do not use any abrasives – this may cause the LCD display to become obscured.
4.3 Probe Replacement
The probe should be returned to Michell Instruments annually for recalibration. This will ensure continued traceability and will verify that it is still performing within its specified accuracy.
4.4 Batteries
When the battery charge indicator icon on the display is empty, the batteries should be replaced (see Section 2.3). Always install 3 new batteries of the same type.

Appendix A

Technical Specifications

HYGROMETER

Performance

Measurement Units| I WoRH, 0C / °F Ta, 0C / °F Td, g/m3, 0C / °F Tw
Mechanical Specification
Ingress Protection| IP54
Hygrometer Housing Material| Molded polymer housing ABS + rubber surround
Weight| 300 g (10.58 oz)
Display Resolution| Graphic LCD 128 x 64 pixels
Electrical Output/Input
Supply Voltage| 4.5 V
(3 x ‘AA’ batteries — provide approximately 150 hours of operation)
Electrical Connections| M9 5-way binder connector

PROBES

Performance

Measurement Range (RH)| 0…100 % rh
Accuracy at 25 °C (77 °F) Temperature| ±0.2 °C (±0.36 °F)
Stability — RH Sensor| ±1% rh/year
Response time — RH Sensor| <10 sec typical (for 90% of the step change)
Measurement & Operating Range (T)
– Fixed and Standard Probe
– Sword Probe
– Remote Probe| -20…+80 °C (-4…+176 °F)
-20…+100 °C (-4…+212 °F)
-20…+150 °C (-4…+302 °F)
Accuracy at 25 °C (77 °F) Humidity
– Fixed Probe
– Remote Probe| ±2% RH (10…90% RH)
±2% RH (5…95% RH)
Mechanical Specification
Weight| Fixed Probe
Standard Probe
Sword Probe
High Temp 300mm Probe
High Temp 500mm Probe| F
SPR
SWPR
HTPR300
HTPR500| 30g (1.06 oz) 90g (3.17 oz) 500g (1.1 Ib) 380g (13.4 oz) 620g (1.37 Ib)

Appendix B

Quality, Recycling & Warranty Information

Michell Instruments is dedicated to complying to all relevant legislation and directives. Full information can be found on our website at: www.michell.com/compliance
This page contains information on the following directives:

• Anti-Facilitation of Tax Evasion Policy
• ATEX Directive
• Calibration Facilities
• Conflict Minerals
• FCC Statement
• Manufacturing Quality
• Modern Slavery Statement
• Pressure Equipment Directive
• REACH
• RoHS3
• WEEE2
• Recycling Policy
• Warranty and Returns

This information is also available in PDF format.

Appendix C Analyzer Return Document & Decontamination Declaration

Decontamination Certificate
IMPORTANT NOTE: Please complete this form prior to this instrument, or any components, leaving your site and being returned to us, or, where applicable, prior to any work being carried out by a Michell engineer at your site.

Instrument| | Serial Number|
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Warranty Repair?| YES| NO| Original PO #|
Company Name| | | Contact Name|
Address
Telephone #| | E-mail address|
Reason for Return /Description of Fault:
Has this equipment been exposed (internally or externally) to any of the following?

Please circle (YES/NO) as applicable and provide details below

Biohazards| YES| NO
Biological agents| YES| NO
Hazardous chemicals| YES| NO
Radioactive substances| YES| NO
Other hazards| YES| NO
Please provide details of any hazardous materials used with this equipment as indicated above (use continuation sheet if necessary)
Your method of cleaning/decontamination
Has the equipment been cleaned and decontaminated?| YES| NOT NECESSARY
Michell Instruments will not accept instruments that have been exposed to toxins, radioactivity, or bio-hazardous materials.  For most applications involving solvents, acidic, basic, flammable or toxic gases a simple purge with dry gas (dew point <-30°C) over 24 hours should be sufficient to decontaminate the unit prior to returning.

Work will not be carried out on any unit that does not have a completed decontamination declaration.

Decontamination Declaration
I declare that the information above is true and complete to the best of my knowledge, and it is safe for Michell personnel to service or repair the returned instrument.
Name (Print)| | Position|
Signature| | Date|

http://www.michell.com

References

• Michell Instruments, Dew Point, Humidity and Oxygen Specialists
• Quality, Recycling, Compliance & Warranty Information - Michell Instruments

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