GAOTek Dew Point Meter for Gas Humidity (High Precision, Storage)

This Dew Point Meter for Gas Humidity (High Precision, Storage) is designed to measure gas humidity with wide measurement range and can store upto 580 measurement results.




GAOTek Dew Point Meter for Gas Humidity (High Precision, Storage) is designed to measure gas humidity with wide measurement range and can store upto 580 measurement results. It adopts mirror condensation dew point method to measure the dew point. With improved service life and stability in measurement, the device adopts measuring circuit with high precision and control algorithm. It helps in detecting the dew point value of air as humidity measurement standard and also judges if the moisture content of the gas effects the production, which also ensures production safety. The device supports equilibrium time of 3 to 6 minutes. It provides DC 14.8V 20AH batteries and has a power of 48 W with a quick response time. The device is used for online detection of industrial and agricultural production and is widely used in many fields such as measurement, meteorology, aerospace, petroleum, chemical, armaments factories.

Key Features

  • Wide measurement range
  • Components: Optical Unit, Refrigeration Control, Gas Path and Electronic Display
  • Reasonable distribution
  • Strong and durable; easy to operate
  • Electronic Display: TFT 4.2 color LCD touchscreen display
  • Display sensitivity: ± 0.1 °F
  • Stores historical data
  • Alarm : Gas flow abnormality alarm & Mirror checked exception alarm
  • Power supply time: ≥ 6 hours
  • Ease in operation
  • Reasonable distribution, small size, strong and durable.

Technical Specifications

Measurement Principle Cold mirror principle
Measurement Scope -76 °F ~ 50 °F (-60 °C ~ 10 °C)  environmental temperature
-76 °F ~ 68 °F  (-60 °C ~ 20 °C) environmental temperature
-67 °F ~ 95 °F (-55 °C  ~ (35 °C) environmental temperature
-58 °F ~ 104 °F (-50 °C ~ 40 °C) environmental temperature
Measuring Accuracy ≤ ± 32.36 °F (≤ ± 0.2 °C)
Repeatability ≤ ± 32.36 °F (≤ ± 0.2 °C)
PPMV Accuracy (computational accuracy) ± 0.1 %
Display Sensitivity ± 32.18 °F  (± 0.1 °C)
Balance Time 3 ~ 6 minutes
Cooling Cooling semiconductor
Sampling Gas Flow 15 ~ 50 L/h
Sample Gas Pressure 0.1 ~ 0.12 MPa
Display TFT 4.2 Color LCD touch screen
Alarm Gas flow abnormality alarm
Mirror checked exception alarm
Response Time 39.2 °F / s (4 °C /s  )Maximum
Power ≤ 48 W
Battery DC 14.8 V  20 AH
Operating Temperature – 4 °F ~ 104 °F (-20 °C ~ +40 °C) (storage, use)
Environmental Humidity Relative humidity of 85 % maximum, no condensation
Weight About 13.67 lbs (6.2 kg)

(W x D x H)

7.72 in x 11.61 in x 10.63 in

(196 mm × 295 mm × 270 mm)

Additional Information


The components mainly include optical unit, refrigeration control, gas path and electronic display.

  • Optical unit: optical unit detection system is composed of luminotron, collection tube etc. and inspects the condensation state of mirror on real time.
  • Refrigeration control: it is composed of mirror, cold dome, base, heat pipe radiator and fan, the mirror is embedded in the cold surface of cold dome which is embedded in the cold dome, radiator is responsible for heat dissipation and the fan is responsible for cooling. High cooling capacity and high efficiency.
  • Gas path: it includes collecting gas joint, sampling tube,  stainless steel needle control valve, fast plug, measuring chamber, flow meter, exhaust pipe, etc. sampling tube adopt polytetrafluoroethylene tube with mm inner diameter and 1mm wall thickness to ensure the measuring precision.
  • Electronic display: adopt TFT 4.2 color LCD touchscreen display, display the temperature of dew point currently measured on real time, graph of equilibrium process, flow and time and so on. Have the functions of alarm, self-inspection, history memory and query, electric quantity and flow detection and calibration.

Measurement Principle

Mirror Dew Point Meter under the constant pressure make the gas flow through closed gas chamber in a certain velocity. The gas measured sweep the cold mirror when flow through dew point measuring chamber. If mirror temperature is higher than the temperature of dew point, the mirror is dry. At this time, the lights emitted by light emitting diode and irradiating the mirror are almost reflected by mirror and then induced by photoelectric sensor that will output photoelectric signal which is used to drive the thermoelectric heat pump(consists of Peltier of Class 4) and refrigerate the mirror after being compared and blown up by control circuit. When the temperature of mirror is decreased to temperature of dew point of gas, dew begin to present on the mirror. When the light are reflected diffusely by mirror after light irradiate the mirror, the optical signal induced by photoelectric sensor are weaken. After the changes are compared and enlarged by control circuit, the thermoelectric heat pump incentive are adjusted to reduce the refrigeration capacity. So that dew on the cold mirror and steam in the gas will be balance through automatic control. The temperature of mirror is induced by platinum resistor (PT100) temperature sensor which is closed to low end of cold mirror so that the temperature of mirror (dew layer temperature) can be accurately measured to obtain the temperature of dew point of gas. It is as humidity measurement standard or is used to judge whether the moisture content of gas affect the production to ensure the production security.

Front panel

It include the following parts:

  1. Measuring head: rotating counter clockwise the tightening cap of measuring head can open the measuring head and then measuring head can be taken down, there are luminotron and collection tube inside the measuring head, cold mirror is located at the central position of measuring chamber and easy to be removed, installed and cleaned.
  2. Gas inlet: gas inlet of instrument is the fixed part of fast join, coordinates with the movable part of fast joint, and is easy to insert and extract and connect with equipment through connecting pipe of gas circuit.
  3. Color LCD touching display: adopt TFT 4.2 color LCD touchscreen display, its function key and display are both on it, display the temperature of dew point currently measured on real time, graph of equilibrium process, flow and time and so on. Simple and easy to use.
  4. Adjusting knob of light intensity: clockwise rotate the knob can strengthen the photoelectric signal, adjust the light intensity make the sensor in optimal working condition and is easy to observe to reduce error.

Back panel

The back panel Mirror Dew Point Instrument is as shown in the following figure:

  1. Power switch: press the power switch, as the system is energized, the instrument starts to work and the initialization and correlation detection are conducted.
  2. Charging interface: the rechargeable battery is internally installed in the instrument, and the instrument can be charged by being connected to the special charger. The battery can continuously work for 6 hours above.
  3. Air outlet: when measuring corrosive or toxic gas, the air outlet is connected to corresponding exhaust pipe to recycle tail gas or dispose it correspondingly; when measuring non-toxic gas, the gas can be discharged directly through the air outlet.

Operating Instruction


  1. The installation and use of Mirror Dew Point Meter shall strictly comply with all operation regulations within all gas systems as well as requirements of the manufacturer of the dew-point instrument.
  2. The staff who use the measurement and debugging of the dew-point instrument shall be fully aware of and acquainted with this equipment and system, and carefully examine the appliances needed for the equipment to ensure those must meet the work and security needs before working.
  3. Before entering the installation and debugging of the system, it is necessary to comprehensively understand the system status and take measures to isolate the parts associated with the instruments under operation.
  4. To guarantee the accuracy of the analyzer, users must use standard gas (supplied by qualified manufacturers) to calibrate this analyzer once a month.
  5. If not immediately used, please keep it in the aluminium box supported by manufacturers and place it in a dry room.


Lift up the device with the handle and place it somewhere smooth and suitable.

  • It requires a ventilated and cool place without flying dust, being waterproof and dustproof, with daylighting and lighting, easy for installation and maintenance as well as data recording, and not easy to touch, keeping away from magnetic field and heat source
  • Do not put it near the laser printer or copying machine
  • Keep the operating environment dry as much as possible
  • Avoid direct sunlight

The preparation before use

  • If not used for long, the instrument must get examined before use to dry the gas circuit of the instrument, all the pipelines and joints, if not kept in the sealed container with the drying agent, must be washed with dry N2 or SF6 gas for 10 minutes, and the flow control valve shall be adjusted to make the gas flow at optimum flow. The moist joint can be dried.
  • Before use, if the mirror check of the main interface fails, one can unscrew the pressure cover of the test probe tightly, take out the test probe and observe if the mirror is clean, if not, it must be wiped clean with neutral cotton paper or degreasing cotton, and then install the test probe on the instrument and screw the pressure cover tightly.
  • The material of gas-taking pipeline will exert some influence on the measurement. Do not use the pipeline of moisture permeability and hygroscopicity, and the stainless steel pipe, copper pipe or the PTFE pipe and polypropylene pipe whose wall thickness is no less than 1mm can be used as the sampling pipe. When the dew-point temperature is tested to be below -76 °F (-60 °C) the stainless steel pipe shall be used, when it is at (-4 °F ~ + 104 °F) (-20 °C ~ +40 °C) the fluorine rubber-pipe can be used. The latex tubing, ordinary rubber hose and thin-wall plastic pipe are not allowed. Improper material will lead to measurement deviation.
  • When connecting the pipes, the quality of the pipes shall be examined, if there are dart, cracks, too many joints and other similar conditions, sample gas leak or infiltration of moisture will occur, directly affecting the accuracy of the test result (the test result is obviously high). When installing the cutting ferrule, details like installing the inner cover well and screwing the card cap need to be treated very carefully and cannot be neglected.
  • Before the test, the gas circuit shall be comprehensively repaired for the leaky part with soapsuds. (By this time the regulator valve on the instrument shall be closed.)
  • The tube connection is as shown in the following figure:

Gas Inlet connection

When connecting the pipes, the leak proofness of the plug and pipeline shall be paid attention to, preventing gas leakage which can cause error influence on the measurement.

Power-on check after installation

First, check the pipe connection, and before the system is not connected, check the gas tightness of all pipelines, if there is any leakage, they shall be sealed again until no leakage exists.

Next, check the circuit, power it up, and the instrument is conducted with all the tests like self-testing and sensor testing, if any problems occur, please check it as prompted; if correct, then the instrument is qualified, and can be put in normal operation.

Operation Interface

Menu structure

The menu tree of Mirror Dew Point Meter is as shown in the figure

Power-on self-test screen

Switch on the power switch of the instrument, and enter the POST screen as shown in the following figure, which shows the information of the manufacturer. The system enters the initialization, sensor testing and the system self-testing, and the display bar displays the test status dynamically.

Power-on screen of Mirror Dew Point Meter

Check completed interface

After the power-on test screen, the instrument shows the all tests completed interface, as shown in the figure.

Gas selection setup interface

When the instrument self-testing is completed, the page switches to display the gas selection setup interface, as shown in the figure.

On this interface, use left-turn and right-turn keys to select the corresponding gas, and the current gas is shown in red, and press Enter key to enter the dew-point measurement interface of the corresponding gas;

The temperature compensation function can be started by pressing the corresponding key, and this function can only be used when testing SF6, for the environment temperature exerts some influence on SF6 electrical equipment and the moisture content in the steel cylinder.

The main testing interface

Select the corresponding test gas, and press Enter key to enter this interface

This interface is the main testing interface, and this interface can show current gas flow, system time, and the temperature value of the mirror surface in real time. Press the “start testing” key to enter the test status, the prompted words on the key turn to “stop testing” from “start testing”.When starting testing, the length of testing begins timing, the temperature of the mirror surface reflects the current temperature value of the mirror surface, and the column “ready” shows the test temperature in real time, and when the test is finished, this column shows the dew-point value; and another column will show PPM value in the measurement in real time. The balanced pointer shows the current balance indicator state dynamically.

Gas type – select the gas whose dew-point is to be measured, and press this key to enter the gas selection interface;
Setup – the system image can be set accordingly. Enter the setup interface and adjust the settings.
Stop testing – the test button shows stop testing in testing state, once pressed this measurement stops; the button turns to the one of start measuring, making it easy to start measuring again or conduct other operations.
Save – to save the data of this measurement so that it can be looked up later on.

In the main interface, the curve block interface can be touched anytime to enter the shift between the curve and value display, and before measuring the mirror of display in real time, it shows the measurement value in real time in the test, and after the test it shows the final dew-point value, the displayed interface after the shift is as shown in the below figure.

Setting interface

Under the condition of untested, press “setting” in main interface will enter into the settings screen.

  • Time setting – Running time, day settings;
  • Language setting – Display setting English;
  • Equipment calibration – Single-point calibration for equipment;
  • Stored query – Keep the data measured before, thus can check historical data;
  • Mirror examination – Automatically checking the cleanliness of the mirror surface and testing the refrigerating capacity;
  • Adjust – Factory debugging for use
  • Return – Finish system settings and return to the main testing interface;

Storage query interface

The storage interface saves and shows time, gas and rate of flow and dew point value and environmental temperature measured earlier. Check previous record through up or down, the selected line is prompted by red, By pressing the delete key the selected record will  be deleted .If you choose delete all option, all the historical record will be deleted and the deleting confirmation dialog box will pop out to confirm before deleting all the records. The return key will return to the main testing interface.

Mirror examination interface

Mirror examination — Execute the check function of the mirror surface;
Refrigeration — Forced refrigeration, the temperature value of the mirror surface will be in real-time display in the process of refrigeration.
Return — Return to settings screen upon the accomplishment of this interface settings;


  1. If ‘return’ key is pressed under the condition of not stop refrigerating, then refrigeration will be shut down automatically by instruments;
  2. The “mirror examination” key just execute single mirror examination function;

Cautions and Maintenance

  1. The tested gas shall be clean gas, otherwise filtration devices (stainless steel microporous filter) shall be installed. Carefully read “common faults and elimination methods” to keep the instrument system in normal standby.
  2. The adoption of electronic flowmeter in this product requires that the regulating valve on quick plug shall be fully closed before ventilation and be opened gradually and slowly after ventilation, the ventilator capacity shall be regulated according to requirement. To avoid the destruction of the electronic flowmeter upon the crush of high pressure gas.
  3. The dew point temperature of the tested sample gas is estimated more than 41 °F (5 °C) below environment temperature to avoid the water contained in sample gas dewing in the inner wall of the pipe, and affect the degree of accuracy of the test.
  4. The inner mirror surface of the sensor shall keep dry and clean, a little absolute ethyl alcohol can be used for maintenance and wiping upon absorbent cotton bar, wipe carefully to avoid scratch on the mirror surface and affect service life of the instrument.
  5. Special attention shall be paid for the dismounting of the upper cover of the sensor due to mirror surface cleaning and testing room requirement.
  • Spin the upper cover and carefully pull the inner core of the sensor out when dismounting the upper cover of the sensor.
  • The mirror surface shall be cleaned and gently wiped with cotton bar or absorbent cotton dipping into absolute alcohol or acetonic and then dry it by pumping into dry gas.
  • NOTICE! The mirror surface shall be protected well.
  • The locating slot shall be carefully in alignment with the locating pin on the pedestal, slowly pull it forward to the bottom and tighten the upper cover when the upper cover of the sensor is installed. Otherwise the air impermeability of the sensor will not meet the requirement, and positive deviation will occur in the testing result due to bad air chamber seal, which cannot meet the requirement of the test.
  1. The precision dew point hygrometer is detecting instruments on normal pressure. When testing the gas to be pressed, the detection shall be made after pressure reduction, the tested exhaust shall be in direct connection with the air to ensure the air pressure of the testing room inside the sensor is 0.1 MPa / cm2, the fluctuation of the air pressure below 0.02 MPa / cm2, thus guarantee the accuracy of the test data.
  2. The tested exhaust (the outlet of the exhaust is on the reverse side of the instrument) shall be discharged to the air through exhaust pipe (ф6 × 0.04 in) (1 mm) with more than 2 meters long to avoid the air penetrating into gas chamber.
  3. The tested exhaust shall be discharged into safe area to avoid the occurrence of blast accidents when detecting flammable gas.
  4. Do not adjust the light intensity adjustment; we are all set up before delivery.


Common troubleshooting

Problems you may run into Methods of resolution
Low-temperature environment, there are condensation phenomenon inside 1. Wash the instrument with dry gas, measurement cannot be taken when the dew point temperature of the tested exhaust is higher than environment temperature.
Fail to inspect the mirror surface 1. Waiting for the temperature of the mirror surface getting back to environment temperature.

2. Looseness of the gas chamber cover.

3. The mirror surface is serious polluted and needs clearance.

Deviation in measurement result 1. Use dry gas to blow pipeline and joint

2. Can only use hydrophobic material such as stainless steel tube, polytetrafluroethylene tube, etc.

3. Exhaust pipe with over 2m long shall be connected when using.

Big differences between two measuring result 1. The flow passage components are not completely dry such as the pipeline, joint, reducing valve, etc. The rate of flow can be properly turned up for a certain time
The sample gas tube is polluted by oil 1. Clean the pipe and joint with agent(such as acetone) and then dry them with compressed air
Air leakage in system 1. Air impermeability of the system, use leak detector or liquid soap
The air flowrate is not stable, the fluctuation of humidity and air pressure is big.


1. Detect the air supply to make sure it stable or not, the measurement of the dew point needs a stable air supply
Unstable dew-point temperature 1. Keep the air course and joint as dry as possible, use dry gas to blow if condition allowed.
The display value of the “dew-point temperature” has been stable, but short-term shock phenomenon occurs by chance and recovers to steady state soon. 1. Check the air flowrate and changes in air pressure and then control them.


Storage: under transportation condition, equipment shall be kept in environment with temperature of 32 °F ~ 104 °F (0 °C ~ 40 °C) and relative humidity < 85% and without oily, corrosive gas or fly ash in the air.

Acceptance and Inspection

Equipment shall be accepted timely and inspected according to packing list for equipment, random accessories and documents. Any possible objections shall be raised within 3 working days.

I.Preparation before measurement

  1. Select right joint and pipeline and dry them.
  2. Close the input control valve and connect the pipeline to mouth of taking gas of the tested gas.
  3. Open the power switch of the instrument, insert the air inflow quick plug into the air inlet of the instrument.
  4. Make sure that the whole gas circuit is sealed well and tighten the gas chamber cover of the sensor.


  1. Start up the instrument and enter into the interface of selecting gas, choose relevant gas to be tested, SF6 gas considers whether open the switch for warming or not.
  2. Enter into the measurement interface after confirmation, press “start to measure” entering into the measurement condition.
  3. Press the key “stop” or automatically stop measurement under automatic mode when the temperature of the mirror surface remains essentially constant(i.e. the balance indicator go into the middle or the curve remains essentially flat).

III. End of measurement

  1. Close the valve for air supply and then close input control valve
  2. Disconnect the pipeline and power off the machine.

IV. Notes for measurement

  1. The connection shall be tightened in the linking process of the pipeline to avoid gas leakage.
  2. Wait for the temperature of the mirror surface returning to above 0 °C after each measurement if many consecutive measurements are needed.
  3. The reducing valve must be connected upon the measurement of cylinder gas, and higher requirements are needed for the degree of drying of the gas circuit and joint, which need longer time washing and ventilation.
  4. The dry gas is needed to blow for half an hour each time before measurement.

Humidity/Dew point/PPM comparison table

Dew point centigrade Dew point Fahrenheit °F The pressure of steam Volume ratio of the PPM water Relative humidity Mass ratio of the PPM water
-150 -238 7*10-15 9.2*10-12 5.7*10-12
-140 -220 3*10-10 4.0*10-7 2.5*10-7
-130 -202 7*10-8 9.2*10-5 5.7*10-5
-120 -184 10*10-8 1.3*10-4 5.4*10-7 8.1*10-5
-118 -180 0.00000016 0.00021 0.0000009 0.00013
-116 -177 0.00000026 0.00034 0.0000014 0.00021
-114 -173 0.00000043 0.00057 0.0000023 0.00035
-112 -170 0.00000069 0.00091 0.0000037 0.00057
-110 -166 0.0000010 0.00132 0.0000053 0.00082
-108 -162 0.0000018 0.00237 0.0000096 0.0015
-106 -159 0.0000028 0.00368 0.000015 0.0023
-104 -155 0.0000043 0.00566 0.000023 0.0035
-102 -152 0.0000065 0.00855 0.000035 0.0053
-100 -148 0.0000099 0.0130 0.000053 0.0081
-98 -144 0.000015 0.0197 0.000080 0.012
-96 -141 0.000022 0.0289 0.00012 0.018
-94 -137 0.000033 0.0434 0.00018 0.027
-92 -134 0.000048 0.0632 0.00026 0.039
-90 -130 0.000070 0.0921 0.00037 0.057
-88 -126 0.00010 0.132 0.00054 0.082
-86 -123 0.00014 0.184 0.00075 0.11
-84 -119 0.00020 0.263 0.00107 0.16
-82 -116 0.00029 0.382 0.00155 0.24
-80 -112 0.00040 0.526 0.00214 0.33
-78 -108 0.00056 0.737 0.00300 0.46
-76 -105 0.00077 1.01 0.00410 0.63
-74 -101 0.00105 1.38 0.00559 0.86
-72 -98 0.00143 1.88 0.00762 1.17
-70 -94 0.00194 2.55 0.0104 1.58
-68 -90 0.00261 3.43 0.0140 2.13
-66 -87 0.00349 4.59 0.0187 2.84
-64 -83 0.00464 6.11 0.0248 3.79
-62 -80 0.00614 8.08 0.0328 5.01
-60 -76 0.00808 10.6 0.0430 6.59
-58 -72 0.0106 13.9 0.0565 8.63
-56 -69 0.0138 18.2 0.0735 11.3
-54 -65 0.0178 23.4 0.0948 14.5
-52 -62 0.0230 30.3 0.123 18.8
-50 -58 0.0295 38.8 0.157 24.1
-48 -54 0.0378 49.7 0.202 30.9
-46 -51 0.0481 63.3 0.257 39.3
-44 -47 0.0609 80.0 0.325 49.7
-42 -44 0.0768 101 0.410 62.7
-40 -40 0.0966 127 0.516 78.9
-38 -36 0.1209 159 0.644 98.6
-36 -33 0.1507 198 0.804 122.9
-34 -29 0.1873 246 1.00 152
-32 -26 0.2318 305 1.24 189
-30 -22 0.2859 376 1.52 234
-28 -18 0.351 462 1.88 287
-26 -15 0.430 566 2.30 351
-24 -11 0.526 692 2.81 430
-22 -8 0.640 842 3.41 523
-20 -4 0.776 1020 4.13 633
-18 0 0.939 1240 5.00 770
-16 3 1.132 1490 6.03 925
-14 7 1.361 1790 7.25 1110
-12 10 1.632 2150 8.69 1335
-10 14 1.950 2570 10.4 1596
-8 18 2.326 3060 12.4 1900
-6 21 2.765 3640 14.7 2260
-4 25 3.280 4320 17.5 2680
-2 28 3.880 5100 20.7 3170
0 32 4.579 6020 24.4 3640
2 36 5.294 6970 28.2 4330
4 39 6.101 8030 32.5 4990
6 43 7.013 9230 37.4 5730
8 46 8.045 10590 42.9 6580
10 50 9.209 12120 49.1 7530
12 54 10.52 13840 56.1 8600
14 57 11.99 15780 63.9 9800
16 61 13.63 17930 72.6 11140
18 64 15.48 20370 82.5 12650
20 68 17.54 23080 93.5 14330