GAOTek Chilled Mirror Dew Point Instruments (Accurate Measurement)

Additional Information

 Ordering Information

 Standard configuration of the equipment includes a prepositive tight pressure measuring probe with three-stage Peltier cooling. As for the corrosive gas, pipeline should be made of PTFE or stainless steel. There is a built in electronic flow meter, monitoring sample gas flow.

GT00XA00ZZ-A is specifically designed for air dew point measurement. It is applicable to standard reference for electronic component durability, dew point control for firing furnaces, dew point control for fuel cell test system, etc.

GT00XA00ZZ-B is especially for the measurement of Sulfur Hexafluoride (SF6).

GT00XA00ZZ-C is a standard type. It applies to standard reference for laboratory calibration, moisture control for ceramic firing furnaces, and humidity control for thermo-hygrostat chamber.     

 GT00XA00ZZ-D is a high-end type. It is suitable for moisture control of drying process, production process of lithium ion battery, measurement of gas with low dew point.

NOTICE:  The application above is for reference only, model selection depends on the specific situation.

The standard configurations of GT00XA00ZZ-B (SF6) dew point instrument are as follows:

• Main Unit
• Inlet Tube (FEP, 3 m), With Connector
• Instruction Manual
• Packaging Box
• Check the mirror condition, the Mirror Check Indicator should be in the middle of the clean area.
• Press the Mode Conversion Key to ME Mode. The device begins to chill down to the dew point, the Mirror Check Indicator moves toward the contaminated area.
• Wait for the reading on the Dew Point Indicator stable.

Focus: When testing more than one spot, it is necessary to confirm every spot. Because in the environment with high humidity, when the measuring spot is changed, the gas sampling tube loop and the ambient air are still closed.

Measurement Principle:

The measurement probe mainly consists of

• Peltier-Battery (Thermoelectric heating pump) (1), Mirror (2), Pt-100 Sensor (3).
• The temperature sensor is inside the mirror, connected with the refrigeration side of Peltier-Battery.
• The heat generated by refrigeration of Peltier-Battery is rejected by the Cooler (6) and the adjacent Ventilator (7).
• Dew point detection is carried out by the optical system consists of Lamp (4) and photosensitive resistance LDR (5).
• The Peltier Controller (15) process signals generated by the photosensitive resistance and transmit them to the Peltier Output Stage (14), so as to form a layer of dew on the mirror. Temperature signal produced by PT-100 Sensor (3) is transmitted to the Dew Point-Temp. Amplifier (11).
• The measurement result is displayed on the Dew Point-Indicator ℃ DP (12).
• The slight and tiny difference in brightness of Lamp (4) will actually change the measurement result.
• In order to avoid a mistake, Lamp Stabilizer-Block (9) provides an accurate voltage supply.
• The additional Stabilizer-Block (10) changes AC to DC and generates the required ±15 V DC voltage for sub-controlling.
• The Power Supply (8) is composed of transformer and rectifier.

Panel Description

Front Panel

4-1. Power Switch Key – Press the Power Switch Key to switch on the instrument.

4-2. Unit Conversion Key – Press the Unit Conversion Key to perform unit conversion.

4-3. Dew Point Indicator (℃ Dew Point) – The Dew Point Indicator display the actual dew     point temperature in centigrade.

4-4. Test Cooling Key – The key is used to test the accuracy of instrument at 0 ℃.

4-5. Mode Conversion Key (CH / ME) – The key mode conversion (CH / ME). In the mode of ME, the Peltier Cooling System begins to chill down. While in the mode of CH, the Peltier Cooling System stops working.

4-6. Flow Indicator – Indicating light display the flow in L/HR (Litre/Hour). If the flow is less than 15 L/HR, the indicator light blinks at 15. If the flow is greater than 60 L / HR, the indicator light blinks at 60.

4-7. RS – 232 Interface – Using RS-232 data cable for connection, data transmission between the instrument and PC is available.

4-8. Light Intensity Hole – In the CH Mode after the mirror is wiped up, if the light of Mirror Check Indicator is not in the middle of the clean area, insert a screwdriver into the hole for adjustment, so as to turn the indicating light to the clean area. (Area division of Mirror Check Indicator see 4-10)

4-9. Gas Selection Key – When measuring different kinds of gas, press the key for selection.

4-10. Mirror Check Indicator – Inside the measurement probe, the light, generated by luminous tubes and reflected by the mirror, is transmitted to the photosensitive resistance, the indicator is divided into clean area and contaminated area (the left 7 grids represent contaminated area, the right 3 grids represent clean area). If the indicator lights in the middle of the clean area, indicating total reflection, the mirror is clean when condensing. The weaker is the reflected light (the higher degree is the mirror polluted), the more close to the contaminated area is the indicator. When the instrument is in the CH Mode, the indicator light must be in the middle of the clean area. If contaminated, the mirror must be cleaned, then adjust the light intensity hole for correction. When the instrument is in the ME Mode, the mirror starts to chill down. When the temperature drops to dew point, dew or frost column crystal is formed, the indicating light moves to contaminated area from clean area.

4-11. Gas Inlet – The Gas Inlet Tube is connected with the Connector on the device.

4-12. Flow Control Valve – The valve controls present gas flow.

4-13. Measurement Probe – After the loop pressure of gas in the instrument is released, anti-clockwise rotate the measuring probe to open it, the internal PTFE tube is also removable. The Photosensitive Resistor is connected on left, and the Lamp is connected on the right. The Mirror is installed between the gas inlet (top) and the gas outlet (bottom).

4-14 – Ventilator – The Ventilator is used to cool down the Measurement Probe. When the device is electrified, the Ventilator rotates continuously.

4-15. Gas Outlet – For the measurement of air and harmless gas, the gas outlet is open to the atmosphere. For the measurement of corrosive gas or toxic gas, it is better to take measurement in closed loop, the gas outlet should be connected with the corresponding gas tube.

4-16. DC Power Output 12V – The output of DC power supply.

4-17. Power Socket – For the connection between the instrument and power source.

Start-up Commissioning

 Device State

If the instrument has not been used for a period of time, it is necessary to adjust before use. All of the tubes and the connecting sleeve can-not be sealed or filled with dry gas, however, must be blown for 10 minutes with dry N2, O2 or SF6 (the maximum pressure 10 bar / Mpa). Open the Flow Control Valve completely, slowly open the Sleeve Control Valve for 40L/HR gas flow required. Use the electrical drier to blow-dry connectors and connections.

Mirror Cleaning

Before use, swab the mirror with neutral tissue paper or cotton (without any solvent). And then reinstall the front part of the Measurement Probe, connect the power supply and switch on, press the Mode Conversion Key to CH Mode. The indicating light should be in the middle of clean area. If necessary, adjust the light intensity hole so that the indicating light is in the appropriate position.

 Test Gas Supply System (Sample Gas Injection Tube)

The material selection of gas injection tube and proper installation are important.

Improper material of gas injection tube effects gas temperature, causing incorrect test results. * Rubber, Nylon or PVC, material which is permeable to water vapor is not available.

• When tested dew point is as low as – 40 °F (- 40 ℃), Polyethylene or Brass tube is available.
• When the maximum operating pressure is 10 bar, use PE (Polyethylene), FEP or PTFE tube.  (Diameter 0.16 in x 0.24 in (4 mm x 6 mm))
• The maximum operating pressure for Stainless Steel tube is 250 bar (25 Mpa).

The sampling gas injection tube should be as short as possible. The temperature of tube must be higher than the dew point of the inlet gas, even in extreme conditions (condensation in tube = false measurement).

Testing Field Installation A typical installation for SF6 measurement is as below.

 A typical installation for GT00X00ZZ-B (SF6) measurement is shown below:

Measurement

Preparation

Device Connection:

Firstly connect the instrument with the sampling spot, and plug it in.

Measurement under System Pressure:

• Close the Flow Control Valve fully.
• Open the Sleeve Control Valve fully.
•  Open the Flow Control Valve slowly till the gas flow indicated gets in the range of 30-40 L / HR.

Measurement under Barometric Pressure

•  Close the Sleeve Control Valve fully.
• Open the Flow Control Valve fully.
• Open the Sleeve Control Valve slowly till the gas flow indicated gets in the range of 30– 40 L / HR.

Measurement

• Press the Power Switch Key to switch on.
• Press the Mode Conversion Key to the CH Mode.
• Check the mirror condition, the Mirror Check Indicator should be in the middle of  the clean area.
•  Press the Mode Conversion Key to ME Mode. The device begins to chill down to the dew point, the Mirror Check Indicator moves toward the contaminated area.
• Wait for the reading on the Dew Point Indicator stable.
•  Read. Focus: When testing more than one spot, it is necessary to confirm every spot. Because in the environment with high humidity, when the measuring spot is changed, the gas sampling tube loop and the ambient air are still closed. It takes a little longer time for ultra-low dew point temperature measurement. In normal measurement, the reading will shock 1-3 times around the real dew point

Refrigeration Check

A simple test can be used to check the measurement accuracy. If the measured results and predicted values differ too far, or consider that the instrument has fault. It is necessary to test.

Procedure:

1. Disconnect the gas sampling tube or close the Sleeve Control Valve.
2. Fully open the Flow Control Valve.
3. Remove the Measurement Probe.
4. Plug in and switch on.
5. Press and hold the Test Cooling Key and drop the mirror temperature in the range of – 13 °F to – 22 °F (- 25 ℃ to -30 ℃) (see the Dew Point Indicator).
6. Blow at the mirror to frost.
7. Release the Mode Conversion Key to rise the mirror temperature.
8. If the mirror temperature rises too fast, the current mirror temperature indication will lag behind. Therefore, rise the mirror temperature slowly before reaching 32 °F (0 ℃), and cool for a while.
9. Watch the Mirror and the Temperature Indicator carefully. The frost layer on the Mirror should be melted into drops of water at 0 ℃. If this phenomenon appears, the device indicates temperature correctly

 Mirror Check And Lamp Brightness Adjustment

The Mirror must be cleaned regularly. When the Mirror Check Indicator is in the contaminated area (in the Mirror Check Mode), indicating the Mirror is contaminated, it is necessary to clean the Mirror. Either Lens tissue or cotton is available to wipe the Mirror, while wet towel is not available. If necessary, high purity alcohol is admitted. For the light source Lamp and the photosensitive resistance LDR, soft cotton swab (Q shaped swab) is available.

Procedure:

1. Close the Sleeve Control Valve.
2. Open the Measurement Probe.
3. Clean the Mirror.
4. Re-install the Measurement Probe.
5. If the Mirror Check Indicator light in the clean area (clean), the cleaning process is completed. If it is still in the contaminated area or edge of the clean area, continue to the following operation (6).
6. Adjust the Light Intensity Hole so that the Mirror Check Indicator light is in the middle of the clean area.
7. If the operation does not work (the Light Intensity Adjusting Hole does not make a difference), it is necessary to clean the Lamp and the LDR photosensitive resistance inside the Measurement Probe.

Fault Analysis

Moisture Content Conversion of (SF6) (PPM)

Note: 1 Mpa = 10 bar, 1 ppmg = ppmv / 8.1

The Relationship between Gas and Pressure (SF6).

When the gas is in the temperature below the condensing point, dew point measurement is not available. This gas condenses on the mirror, the figure below indicates the relationship between gas (SF6) and pressure.