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Advanced new technology with high accuracy and unparalleled freedom from artifacts

Concerned or frustrated with the performance of your current humidity measurements?  Wondering why measuring humidity and temperature can be so vexing and difficult, with accuracy specs all over the map, some believable some un-believable?  Here’s what we’ve done about it:

We’ve created an advanced new electronic system for measuring humidity and temperature.  It’s called True RH© technology.  True RH delivers highly accurate RH measurements while compensating for offset drifts, ambient temperature drifts, changes in circuit board capacitance, changes in RH sensor conductance, amplifier gain drift, amplifier input impedance drift… and much more.

The TM-450A measures the pure capacitance of the RH sensor (a capacitive humidity sensor) and the pure resistance of the temperature sensor (a thermistor). The TM-450A’s patented circuitry (US 9,360,445) is a very high performance impedance analyzer, capable of measuring the capacitive and resistive components of each sensor to better than 1 part in 10,000 accuracy. The performance of these underlying sensor measurements exceed that of most laboratory grade instruments.

Measured RH is reproducible to 0.1%, with noise equivalent humidity of less than 0.1% RH. Absolute RH accuracy is ±1.3%. Measured temperature is reproducible to 1 deg (C or F), with noise equivalent temperature of less than .01 deg C. Absolute temperature accuracy is ±1 degC. 

The TM-450A tolerates condensing conditions. It actually reads moisture levels in excess of 100% RH.

We've reduced the hysteresis of the RH sensor to ±1% RH. There is no longer the usual errors seen in other products at the high and low ends of the RH range.

Each TM-450A is individually calibrated with a 5 point cal procedure using a NIST traceable two pressure humidity generator. A two pressure humidity generator is considered the gold standard for accurate and reproducible humidity calibration.

When your TM-450A displays a humidity and a temperature, you be assured the values are real, not an artifact of the sensor electronics.


Designed for your regulatory and QC environment

You need to measure RH and temperature. You want it validated and alarmed. You want it to be accurate, and you want it to be easy. If the success of your processes depend on these measurements, trust the TM-450A.

It’s easy to read, easy to interpret, no buttons to push, nothing to reset, just read the numbers. A quick glance and you will know if your monitored environment is within limits.

Measurements you can trust and verify: The TM-450A was built to be re-calibrated on a routine basis. Choose standard cal points or order custom cal points tailored to your QC requirements. The TM-450A is NIST traceable.

Min/Max for RH and temperature are continuously displayed. The time interval for Min/Max measurement can be set to 8, 16, 24 hours or 7 days.  There is no reset button to fuss with or that can be accidentally pushed at the wrong time. There is no guessing as to when a particular Min or Max event occurred.

Trend indicators for both RH and temperature show you where your controlled environment is heading.

Audible and visual alarms alert you of extreme conditions including: excessive temperature, excessive temperature change, excessive humidity, excessive humidity change, condensing conditions, and wet conditions.

The TM-450A can be customized to your particular environment: Along with cal points, Alarm points, Min/Max measurement intervals, and trend measurement intervals can be specified by you at the time of purchase or changed when re-calibrated. Adjustable parameters can even be permanently locked out to prevent changes by un-authorized users.

And, now, you can stay up to date with the best technology available: TM-450A units which are re-calibrated on a yearly basis receive a lifetime warranty, free maintenance, and free hardware and software upgrades.

Designed and manufactured in the USA


High Reliability

The TM-450A is built for tough industrial environments.

It is protected from dust and water intrusion to IP67 level (1 meter submersion in water for 30 minutes).

It has a rugged ABS/Polycarbonate blend case and a thickened polycarbonate display cover. It has been drop tested to 2 meters.

The case is compatible with many surface applied cleaning and disinfecting solutions: Wipe down tests have been done with dilute Ethanol, Propanol, Quaternary Ammonia, and Hypochlorite solutions.

The sensors are protected with silicone o-rings, vapor permeable Teflon vents, and splash guards.

The TM-450A even works in condensing conditions. Not only do the RH and temperature sensors tolerate condensing conditions, the measurement electronics are designed to easily handle the unusual electronic character of the sensors that occur when liquid moisture is present. In addition, electronic components and circuitry are coated with a high integrity moisture proof film, ensuring reliable operation in the presence of condensation. The TM-450A actually reads flawlessly through the condensing point and beyond! It can be used in refrigerators, cold rooms, and chiller units without fear of water condensation harming the unit, changing the calibration, or affecting the RH or temperature measurement.

System self-test and sensor verification are done automatically on a continuous basis. Any faults discovered are flagged on the display for the user.

Main battery charge level is tested every 10 minutes. A low battery condition is announced to the user with ample time for battery change out. The TM-450A has multiple alarm levels for both low battery, and nearly discharged battery conditions.

Main batteries are hot swap-able!  A backup battery ensures no loss of data during main battery change out. Backup battery lifetime is approximately 10 years.

Tested to FCC and ICAN emission standards.

Flame retardant case meets or exceeds UL94-V0

1 year warranty. Lifetime warranty with yearly calibration.


User Friendly

The TM-450A is simple. There are no controls to adjust or set, no menus, and no min/max to reset. Everything you need is right in front of you. Just read the numbers. It’s a data logger without the hassle!

All parameters you need are displayed simultaneously: RH, RH max, RH min, RH trend, Temperature, Temperature max, Temperature min, and Temperature trend.

Min, Max, and Trends can be read continuously from the display. There are no reset buttons for Min and Max. The TM450A always shows the minimum and maximum for both RH and temperature over the last 8, 16, 24 hours, or 1 week period.

The TM450A has integrated RH and Temp sensors. There are no cables to worry with.

It works flawlessly in condensing conditions.

The TM450A has a heart of green. Ultra-low power design ensures long battery life. All components meet international ROHS standards.

It uses 2 standard 1.5V AA batteries. With alkaline batteries, battery life is approximately 1 year.

Wall mount or table-top stand. There are also handy screw bosses on the TM-450’s case for your custom mounting needs.



  • Food processing
  • Ideal for your HACCP or ISO22000 program for monitoring critical limits in RH and temperature
  • Fruit, nut, vegetable, grain storage and transport
  • Wine cellars and storage
  • Greenhouse management
  • Lasik operating rooms and digital mammography suites
  • CLIA compliance in clinical laboratories
  • CMS compliance for RH and temperature monitoring in the operating and other hospital areas
  • Pharmaceutical processing
  • Blood Banks
  • ESD controlled environments
  • Computer server farms and data centers
  • Museums, museum micro-climates, archival collections, and preservation
  • Libraries and film archives
  • Ship cargo holds
  • Basements and other potentially high moisture storage areas
  • HVAC monitoring and IAQ (internal air quality) verification
  • Monitoring intermittent high moisture areas such as bathrooms, showers, and wash-down areas
  • Condensation risk assessment
  • Textile manufacture
  • Paper manufacture
  • Printing
  • Photographic processing 




Sensor Type Capacitive
Range 0 - 100 %RH
Resolution 0.1 %RH
Condensing Condtions OK
Calibration NIST traceable 5 point calibration (including hysteresis compensation)
Overall Accuracy (StdDev) 1.27 %RH   (range 0-80)
1.41 %RH   (range 80-100)


RH Accuracy Components:

source %RH (0-80) %RH (80-100)
calibrator accuracy 0.30 0.70
system noise 0.01 0.01
humidity sensor temperature 0.10 0.10
humidity sensor accuracy 0.50 0.50
hysteresis (90 to 50 %RH, 2 hrs) 1.0 1.0
drift (per year) 0.50 0.50
__________ __________
Overall Accuracy  (StdDev)      1.27 1.41



Sensor Type Thermistor
Range -20C to +50C   (-4F to +122F)
Resolution 1 degC    (1 degF)
Condensing Conditions OK
Calibration NIST traceable 2 point calibration
Overall Accuracy (StdDev) 0.10 degC


Temperature Accuracy Components:

source degC
calibrator accuracy 0.01
system noise 0.01
thermistor accuracy 0.1
drift (per year) 0.01
Overall Accuracy  (StdDev)      0.10


Displayed Simultaneously: Relative Humidity (%RH)
Temperature (degC or degF)
Max %RH
Min %RH
Max Temperature
Min Temperature
%RH Trend  Arrow (up, steady, down)
Temperature Trend Arrow (up, steady, down)
Low battery, Condensing conditions, and System error
Measurement Intervals: Humidity sample rate 4 per minute
Temperature sample rate 4 per minute
Time windows for min and max 8hr, 16hr, 24hr, or 7days
Time windows for RH and temperature trends 2hr, 4hr, 8hr, or 1day
Alarms: Condensing conditions, current RH
Condensing conditions, RH max
Condensing conditions, RH min
Wet conditions, current RH
Wet conditions, RH max
Wet conditions, RH min
Temperature <-20C  or  >50C
Temperature max <-20C  or  >50C
Temperature min <-20C or  >50C
Excessive RH trend (up or down)
Excessive Temperature trend (up or down)
Main battery low
Main battery very low
Main battery removed
System Error
Display Type High contrast FSTN LCD
Display Protection 20 mil polycarbonate overlay + impact absorbing gap
Case material ABS / Polycarbonate blend
Fire retardancy All external case materials rated UL94V0 or better.
Dust and water ingress: Case is sealed with silicone o-rings.
Case is vented with teflon vents.
Sensor is protected by a waterproof Teflon membrane.
Sensor is protected from direct water impingement with a splash guard.
PC board is protected with a silicone conformal coating.
IP67 classification
Batteries 2 AA alkaline (1.5V), fused, reverse voltage protected.
Batteries are hot swappable No loss of average, min, max, or trends during battery change.
Battery life Approximately 1 year (for alkaline)
Backup battery 3V lithium ion 
Audible alarm Piezo speaker
Dimensions 5.7w x 2.9h x 1.0d in.   (145 x 75 x 25 mm)
Weight (with batteries) 6.8 oz (194 gm)
Approvals ICAN/FCC Class B, CE Group 2 Class B (EN55011), VCCI Class B
Manufacture Made in the U.S.A.
Warranty 1 year from date of purchase



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