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Environmental Monitoring Instruments Buying Guide

Ever wondered why some freshly painted bridges rust within a few years while others seem to last for decades? A key factor is controlling the environment during coating application.

Explore how environmental conditions like temperature and humidity impact the long-term performance of coatings on steel structures. By equipping yourself with the right environmental monitoring instruments, you can ensure optimal pre-treatment and application conditions, leading to long-lasting protection for your steel assets.

Check out BlastOne’s full inventory of DeFelsko Inspection Instruments.

 

 

 

Name Available for Rent Best Scenarios Benefits Disadvantages Options Product Page
PosiTector Dew Point Meter
(DPM)		 Yes Digital dew point meter – Measures and records climatic conditions including:

  • Relative humidity (%RH)
  • Air temperature
  • Surface temperature
  • Dew point temperature
  • The difference between surface and dew point temperatures (Delta)
  • Wind speed
  • Wet bulb temperature
  • NEW Larger 2.8″ impact resistant color touchscreen with redesigned keypad for quick menu navigation
  • NEW Weatherproof, dustproof, and water-resistant—IP65-rated enclosure
  • Fast response precision sensors provide accurate, repeatable readings
  • Auto Log mode records environmental parameters at user selected time intervals
  • Requires adequate time to acclimate to operating environment
    • Mere seconds for similar environments but can take up to 30 minutes when moving between environmental extremes
  • Not recommended for operations inside an oven
  • Integral Probe with Direct Contact Surface Temperature Sensor
  • Integral Probe with Infrared Surface Temperature Sensor
  • Integral Probe with K-type Cabled Surface Temperature Sensor
  • Integral Probe with Wind Speed Sensor
  • Cabled Probe with 1/2″ NPT Threads (for compressed air)
PosiTector Dew Point Meter Logger
(DPML)		 No
  • Attaches to steel structures to measure and record environmental parameters independently for up to 200 days
  • Measures and records climatic conditions including:
    • Relative humidity
    • Air temperature
    • Surface temperature
    • Dew point temperature
    • Difference between surface and dew point temperatures
    • Wet bulb temperature
  • Fast response, precision sensors provide accurate, repeatable readings
  • Environmentally sealed enclosure – weatherproof, dustproof, and shockproof—meets or exceeds IP65
  • Internal memory storage of 10,000 datasets (60,000 readings)
  • Not recommended for operations inside an oven
  • Battery life varies depending on logging intervals and is reduced while connected to the PosiTector app or instrument
Positector Infared Thermometer
(IRT)		 No
  • Measures surface temperatures in areas where conventional sensors will not work including hard to reach areas, moving parts, freshly sprayed powder coating, and objects whose temperatures are above the range of direct contact sensors
  • Button-activated laser pointer for accurate targeting
  • Selectable emissivity values—choose from 7 preset material options, set a custom emissivity value, or adjust to a known temperature
  • Statistics Scan mode—continually displays/updates average, standard deviation, min/max surface temperature and number of readings while measuring one reading per second
  • 5.7:1 distance to spot ratio—ideal for measuring large areas
  • Smart Trend indicators identify rising, falling or stable readings
  • Measures only surface temperature
  • Impacted by surface emissivity (material’s ability to emit infrared energy) – can affect accuracy
PosiTector Dew Point Meter
(DPM)		 PosiTector Dew Point Meter Logger
(DPML)		 Positector Infared Thermometer
(IRT)
Available for Rent Yes No No
Best Scenarios Digital dew point meter – Measures and records climatic conditions including:

  • Relative humidity (%RH)
  • Air temperature
  • Surface temperature
  • Dew point temperature
  • The difference between surface and dew point temperatures (Delta)
  • Wind speed
  • Wet bulb temperature
  • Attaches to steel structures to measure and record environmental parameters independently for up to 200 days
  • Measures and records climatic conditions including:
    • Relative humidity
    • Air temperature
    • Surface temperature
    • Dew point temperature
    • Difference between surface and dew point temperatures
    • Wet bulb temperature
  • Measures surface temperatures in areas where conventional sensors will not work including hard to reach areas, moving parts, freshly sprayed powder coating, and objects whose temperatures are above the range of direct contact sensors
Benefits
  • NEW Larger 2.8″ impact resistant color touchscreen with redesigned keypad for quick menu navigation
  • NEW Weatherproof, dustproof, and water-resistant—IP65-rated enclosure
  • Fast response precision sensors provide accurate, repeatable readings
  • Auto Log mode records environmental parameters at user selected time intervals
  • Fast response, precision sensors provide accurate, repeatable readings
  • Environmentally sealed enclosure – weatherproof, dustproof, and shockproof—meets or exceeds IP65
  • Internal memory storage of 10,000 datasets (60,000 readings)
  • Button-activated laser pointer for accurate targeting
  • Selectable emissivity values—choose from 7 preset material options, set a custom emissivity value, or adjust to a known temperature
  • Statistics Scan mode—continually displays/updates average, standard deviation, min/max surface temperature and number of readings while measuring one reading per second
  • 5.7:1 distance to spot ratio—ideal for measuring large areas
  • Smart Trend indicators identify rising, falling or stable readings
Disadvantages
  • Requires adequate time to acclimate to operating environment
    • Mere seconds for similar environments but can take up to 30 minutes when moving between environmental extremes
  • Not recommended for operations inside an oven
  • Not recommended for operations inside an oven
  • Battery life varies depending on logging intervals and is reduced while connected to the PosiTector app or instrument
  • Measures only surface temperature
  • Impacted by surface emissivity (material’s ability to emit infrared energy) – can affect accuracy
Options
  • Integral Probe with Direct Contact Surface Temperature Sensor
  • Integral Probe with Infrared Surface Temperature Sensor
  • Integral Probe with K-type Cabled Surface Temperature Sensor
  • Integral Probe with Wind Speed Sensor
  • Cabled Probe with 1/2″ NPT Threads (for compressed air)

Environmental Monitoring Instrument Videos

Measuring Environmental Conditions and Remote Monitoring with the Dew Point Meter Series

PosiTector DPM Dew Point Meter Overview

PosiTector DPM Webinar

PosiTector SmartLink

What is a Dew Point Meter?

A Dew Point Meter is a crucial tool for paint and coating applicators, measuring and recording key climatic conditions: relative humidity (%RH), air temperature, surface temperature, dew point temperature, the critical Delta T (difference between surface and dew point temperatures), and even wet bulb temperatures.

By monitoring and recording these factors with a handheld, portable Dew Point Meter throughout surface preparation, application, and curing, you can guarantee optimal environmental conditions. This significantly reduces the risk of costly rework and premature coating failure, saving you time and money in the long run.

How is Relative Humidity (%RH) measured?

Relative Humidity (RH) is a critical factor in paint and coating success, affecting solvent evaporation. High RH can slow down drying, potentially leading to defects.

Traditional Methods: The Sling Psychrometer

Previously, measuring RH involved a sling psychrometer (whirling hygrometer). This tool uses two thermometers: a dry bulb and a wet bulb wrapped in a wet sock. Whirling it for 90 seconds cools the wet bulb due to evaporation, creating a temperature difference. This difference, along with dry bulb temperature, is then referenced in psychometric charts for RH. Complex and time-consuming!

Modern Measurements: Electronic Dew Point Meters

Enter the PosiTector DPM Dew Point Meter, a game-changer for humidity and temperature measurement. These multi-functional tools provide instantaneous and continuous readings of:

  • Relative Humidity (%RH)
  • Air Temperature
  • Surface Temperature
  • Dew Point Temperature

This eliminates the need for complex calculations and human error associated with sling psychrometers and lookup tables.

How is dew point measured?

Understanding Dew Point: The Key to Optimal Coating Performance

Dew Point is the crucial temperature where air becomes saturated and moisture condenses on a surface. It depends on both air temperature and relative humidity (RH). In simpler terms, it’s the temperature you need to cool air to for condensation to occur.

For freshly blasted steel, even a thin, invisible layer of moisture trapped between the coating and the steel can cause flash rust and lead to premature coating failure. To prevent this disaster, ISO 8502-4 and SSPC standards recommend keeping the surface temperature at least 5°F (3°C) above the dew point during the three critical stages of painting: surface preparation, application, and curing.

Traditional Methods: Sling Psychrometer and Chilled Mirror Hygrometers

Traditionally, dew point calculation involved a sling psychrometer and complex charts or calculators. These methods were prone to errors, couldn’t monitor continuously, and lacked data storage.

Chilled mirror hygrometers used a chilled mirror, light beam, and light detector to measure dew point.  As the air is cooled, dew would form on the mirror, blocking the light, and indicating that the air has reached the dew point. The overall bulk, fragility, and cost made them impractical for field use in steel structure painting.

The Rise of the Digital Dew Point Meter 

Modern dew point meters like the PosiTector DPM eliminate the complexities of previous methods. They use high-precision sensors to measure surface temperature and relative humidity, instantly calculating dew point. The most practical models include a surface temperature probe to display the all-important delta T: the difference between surface and dew point temperatures. This delta T value is critical for ensuring proper coating adhesion and longevity.

Available Dew Point Meter DPM Models

Select from 5 PosiTector DPM probe models or 1 autonomous PosiTector DPM Logger.

 

 

 

 

Name Surface Temperature Air Temperature Wet Bulb Temperature* Relative Humidity Dew Point Temperature Surface Temperature minus Dew Point Temperature Wind Speed
Integral Probe w/ Direct Contact Surface Temperature Sensor ♦ ♦ ♦ ♦ ♦ ♦
Integral Probe with Infrared Surface Temperature Sensor ♦ ♦ ♦ ♦ ♦ ♦
Integral Probe with K-type Cabled Surface Temperature Sensor ♦ ♦ ♦ ♦ ♦ ♦
Integral Probe with Wind Speed Sensor ♦ ♦ ♦ ♦ ♦ ♦ ♦
Cabled Probe with 1/2″ NPT Threads ♦ ♦ ♦ ♦
Integral Probe with Direct Contact Surface Temperature Sensor ♦ ♦ ♦ ♦ ♦ ♦
Integral Probe w/ Direct Contact Surface Temperature Sensor

Integral Probe with Infrared Surface Temperature Sensor

Integral Probe with K-type Cabled Surface Temperature Sensor

Integral Probe with Wind Speed Sensor

Cabled Probe with 1/2″ NPT Threads

Integral Probe with Direct Contact Surface Temperature Sensor
Surface Temperature

♦

 ♦ ♦ ♦ ♦
Air Temperature ♦ ♦ ♦ ♦ ♦ ♦
Wet Bulb Temperature* ♦ ♦ ♦ ♦ ♦ ♦
Relative Humidity ♦ ♦ ♦ ♦ ♦ ♦
Dew Point Temperature ♦ ♦ ♦ ♦ ♦ ♦
Surface Temperature minus Dew Point Temperature ♦ ♦ ♦ ♦ ♦
Wind Speed ♦

*Wet Bulb Temperature displayed/recorded on PosiTector Advanced (3) models only

Which Dew Point Meter is Right for My Application?

DPM Key Considerations

There are four key decisions when selecting a dew point meter:

  • Identify the environmental parameters that need to be monitored

    Applying coatings to steel structures requires precise control over environmental factors to ensure optimal performance and longevity. Here’s a breakdown of the crucial measurements to monitor:

    • Surface Temperature: This is the most critical factor, as it directly influences condensation. A high-quality surface thermometer is essential for accurate readings. Surface temperature can vary significantly due to direct sunlight, shade, and even the structure’s size and shape.

    • Air Temperature and Relative Humidity (RH): These are interrelated and influence drying times and dew point. Measuring them with a hygrometer or psychrometer allows you to assess the overall drying conditions.

    • Wet Bulb Temperature (for Dew Point Calculation): Traditionally used with psychrometers, this temperature is factored in to calculate dew point.

    • Dew Point Temperature: This is the temperature at which condensation occurs on a surface. Maintaining a sufficient difference between surface temperature and dew point (Delta T) is vital for proper drying and adhesion.

    PosiTector DPM: Your Dew Point and Delta T Solution

    Some advanced dew point meters, like the PosiTector DPM, can measure all the above parameters and calculate Delta T directly. This eliminates complex calculations and ensures you have the most crucial information for successful coating application.

  • Can you easily access the surface? Is it too hot for traditional thermometers?

    Dew point meters equipped with an infrared surface temperature sensor, such as the PosiTector DPM IR can accomplish this measurement while still measuring and calculating other parameters.

  • Do you need to monitor environmental conditions for a short period or track them continuously throughout the project?

    Need Instant Readings or Long-Term Monitoring? PosiTector DPM Has You Covered!

    All PosiTector DPM models provide instantaneous measurements for quick assessments. They also boast an Auto Log mode for continuous monitoring over extended periods.

    Advanced models take it a step further with an enhanced Auto Log mode that automatically powers down the instrument between readings. This maximizes battery life, allowing for up to 8 months of continuous data collection.

    For projects requiring unattended, long-term monitoring, the PosiTector DPM L is the ultimate champion. This compact powerhouse delivers up to 200 days of battery life without compromising accuracy.

  • What are the reporting requirements?

    All PosiTector DPM Standard models can store up to 2,500 datasets. All PosiTector DPM Advanced models can store up to 250,000 datasets or 1,000 batches. The PosiTector DPM L Dew Point Meter Logger can store up to 10,000 datasets (60,000 readings). Software solutions are available for viewing, analyzing, and reporting data.

What Environmental Conditions are monitored with Dew Point Meters?

Depending on which PosiTector DPM model is selected, a dataset can consist of five or more of the environmental parameters below.

Standard models feature storage of 2,500 datasets.
Advanced models can store up to 250,000 datasets.
The PosiTector DPM L can store up to 10,000 datasets.

MEASURES
CALCULATES
RH — Relative Humidity: the amount of moisture in the air expressed as a percent of overall volume
Td — Dew Point Temperature: the temperature at which moisture will begin to form on a surface
Ta — Air Temperature: the temperature of the air
Ts–Td —Delta: the difference between surface and dew point temperatures
Ts — Surface Temperature: the temperature of a surface
Tw — Wet Bulb Temperature
V — Wind Velocity: the speed at which the air is moving (PosiTector DPM A only)

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Frequently Asked Questions

  • When is it safe to paint?

    The difference between the surface temperature and the dew point temperature is the most critical, determining factor for the long-term performance of coatings and linings on steel structures.

    Documents such as ASTM D3276 and the international standard ISO 8502-4 state that the surface temperature must be a minimum of 5°F (3°C) above the dew-point temperature during the critical 3 phases of coating: preparation, application and cure. This minimum separation also helps allow for surface temperature reduction as solvents evaporate or when cold coating materials are applied.

    If the dew point temperature is below this minimum separation, or even if they are close, the risk on moisture forming on the steel surface may be unacceptably high and may lead to coating failure.

  • Why is it important to measure dew point in compressed air?

    When air is compressed, the gasses (oxygen, nitrogen, etc.) become more dense. As a result, the liquid water vapor within that air can easily reach saturation, especially in warmer environments such as factories.

    Some industries monitor compressed air systems for moisture and dewpoint temperatures since moisture can have a negative effect on the adhesion, color, and gloss of spray-applied coatings using compressed air. Wet compressed air can cause damage to components allowing rust and corrosion to build up. Most problems can be avoided by simply monitoring dew point temperatures in compressed air systems.

  • Do DeFelsko instruments require any formal training for use?

    No. DeFelsko instruments are designed for simple operation, feature easy-to-use menus, instruction manuals, and helpful videos. In lieu of demonstration models, we provide FREE technical support via telephone and/or email, and a limited 30-day money back guarantee.

  • Is the PosiTector DPM or DPM L calibrated at the factory?

    The PosiTector DPM and DPM L arrives fully calibrated and ready to measure. A Long-Form Certificate of Calibration traceable to NIST or PTB is included, which documents actual readings taken by your instrument at our calibration laboratory on standards traceable to a national metrology institute. Beware of ‘Certificates’ or ‘Certificates of Conformance’ offered by competitors. These typically do not include actual instrument readings, and are often insufficient to meet common quality requirements.

  • How often should the PosiTector probe be recalibrated?

    PosiTector probes include a Certificate of Calibration showing traceability to NIST or PTB included (Long Form) with each probe—with no expiry or end date. They have no shelf life, therefore the length of time in the field is not a good indicator for recalibration intervals. Many organizations with quality programs and recertification programs require annual recalibrations, and this is a good starting point for most users. DeFelsko recommends that customers establish calibration intervals based upon their own experience and work environment. Based on our product knowledge, data and customer feedback, a one year calibration interval from the date the instrument was placed in service is a good starting point.

  • Is the PosiTector DPM or DPM L suitable for logging temperatures inside an oven?

    We do not recommend our PosiTector DPM for operation in an oven. Delicate internal components and assembly materials are prone to premature damage when subjected to prolonged use in a closed environment with temperatures greater than approximately 50° C. The PosiTest OTL Oven Temperature Logger is ideal for measuring and recording oven temperature profiles,

  • How long does it take the DeFelsko probe or logger to acclimate, and provide accurate measurements in a new environment?

    The PosiTector DPM or DPM L, like other electronic dew point meters, requires adequate time to acclimate to its operating environment. When moving between similar environments, the instrument will stabilize in a matter of seconds. However, when moving between environmental extremes (like between a dry, air conditioned vehicle and the warm, humid outdoors) it can take up to 30 minutes for readings to stabilize.

    If left in a dry environment for an extended period of time, this stabilization process may take longer. To restore the original response time, wrap the sensor in a damp cloth overnight.

  • Is the PosiTector DPM or DPM L suitable for applications with low or negative dew point temperatures?

    The PosiTector DPM provides accurate dew point readings (±3° C) down to -40° C.

    Dew point is a calculated value, based on temperature and humidity. At low negative dew point temperatures, the calculation is highly dependent on relative humidity and changes of ±3% RH (the tolerance of the PosiTector DPM’s humidity sensor) can have a significant impact on the dew point temperature.

    The Dew Point (Td) Accuracy page details the accuracy of the calculated dew point temperature based on the measured temperature and humidity.

  • Will any k-type thermocouple work with the PosiTector DPMS?

    The PosiTector DPMS Magnetic Surface Temperature Sensor can be disconnected from the K-Type thermocouple connector and replaced with any K-type thermocouple.

    DeFelsko offers the following optional k-type sensors:

    • Hand-held Surface Temperature probe: for spot-checking difficult-to-access areas.
    • Liquid Temperature Probe: general purpose probe with stainless steel shaft.

  • How long does it take the DeFelsko probe or logger to acclimate, and provide accurate measurements in a new environment?

    The PosiTector DPM or DPM L, like other electronic dew point meters, requires adequate time to acclimate to its operating environment. When moving between similar environments, the instrument will stabilize in a matter of seconds. However, when moving between environmental extremes (like between a dry, air conditioned vehicle and the warm, humid outdoors) it can take up to 30 minutes for readings to stabilize.

    If left in a dry environment for an extended period of time, this stabilization process may take longer. To restore the original response time, wrap the sensor in a damp cloth overnight.

  • How long does the battery last on a PosiTector DPM L?

    Depending on the logging interval, the battery on a PosiTector DPM L can last several months. For example, at 5 minute intervals the logger will last 120 days. At 1 hour intervals, the PosiTector DPM L will last 200 days. The stated battery life is for unattended logging. Battery life is reduced while connected to the PosiTector app or instrument.

  • What is the operating temperature range of the PosiTector DPM L?

    The operating temperature range of the PosiTector DPM L is -10 to 60° C (14 to 140° F).

  • What is an infrared thermometer?

    An infrared thermometer measures the thermal radiation emitted by an object without requiring contact.

  • How is the PosiTector IRT different than the PosiTector DPM IR?

    Unlike the PosiTector DPM IR, the PosiTector IRT measures surface temperature only. The PosiTector DPM family measures a number of climatic parameters including relative humidity, air temperature and surface temperature allowing it to calculate dew point temperature and the all-important difference between surface temperature and dew point temperature (Ts-Td) — a vital parameter for industrial painters.

    The PosiTector IRT has a larger distance to spot ratio and a button activated laser pointer for precise and accurate surface temperature measurement.

  • What is distance to spot (D:S) ratio and why is it important?

    The distance to spot ratio refers to the relationship between the diameter of the area being measured compared to the instrument’s distance from that area. As the distance (D) from the measured surface increases, the spot size (S) of the area being measured becomes larger.

    The D:S ratio of the PosiTector IRT is 5.7:1. For example, when the instrument is 85 cm (34 inches) from the surface, the spot size will be 15 cm (6 inches) in diameter. The temperature reported will be an average of the temperatures contained within the spot size. The greater the spot size, the more information will be gathered and averaged, giving you a better estimate of the area’s true temperature. A lower D:S ratio is advantageous when measuring large areas.

  • What is emissivity?

    Emissivity refers to a material’s ability to emit infrared energy, compared to an ideal black surface at the same temperature. The PosiTector IRT has built-in emissivity settings for certain materials as well as user-adjustable emissivity options. Select from a list of preset emissivity options, manually adjust the emissivity value or adjust to a known temperature.

    Most organic and painted surfaces have an emissivity of around 0.95. Shiny or reflective surfaces can be difficult to measure with an infrared thermometer, as they tend to reflect ambient infrared energy instead of emitting their own. To compensate for this, cover such surfaces with flat paint or a piece of electrical tape. Allow the paint or tape to acclimate to the surface’s temperature and take a measurement over the paint or tape.

  • Are infrared surface temperature thermometers such as the PosiTector DPM IR and the PosiTector IRT suitable for measuring the temperature of blasted steel?

    Yes, but adjusting the emissivity setting is critical. Depending on surface treatment, metals such as blasted steel can have a broad range of emissivity values. Adjusting to a known temperature (measured by a direct contact surface temperature probe) on a representative sample will assist in obtaining an accurate emissivity value. Some blasted surfaces can reflect nearby sources of infrared energy, impacting results. DeFelsko recommends situational testing be done to determine accuracy.

  • What is measured with an infrared surface temperature probe and what are some typical applications?

    An infrared surface temperature probe measures surface temperature from a distance without contacting the surface. An IR surface temperature thermometer is useful for measuring temperatures in areas where conventional sensors will not work including hard to reach areas and moving parts. Also ideal for measuring on objects whose temperature is above the recommended range for direct contact sensors or when contact with a sensor would damage the surface as is the case for freshly sprayed powder.

    The 5.7:1 distance to spot ratio of the PosiTector IRT will average the temperature over a larger area and is ideal for quickly scanning large steel structures.

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