Valco Instruments Co. Inc. Microvolume Thermal Conductivity Detector Instruction Manual tcd2.p65 Rev 4/12 Printed in USA North America, South America, and Australia/Oceania contact: Europe, Asia, and Africa contact: Valco Instruments Co. Inc. VICI AG International 800 · 367 · 8424 sales 713 · 688 · 9345 tech 713 · 688 · 8106 fax valco@vici.com Schenkon, Switzerland Int + 41 · 41 · 925 · 6200 phone Int + 41 · 41 · 925 · 6201 fax info@vici.
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Table of Contents Introduction Description and Operating Principle ............................................................... 1 Safety Notes and Information ........................................................................ 2 Components of the Detector System ............................................................. 3 Description of Controls and Connectors ......................................................... 4 System Requirements Components Not Included with the Detector System .........
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1 Introduction Description and Operating Principle The Thermal Conductivity Detector (TCD) has been one of the most popular GC detectors since the 1950’s, second perhaps only to the Flame Ionization Detector (FID). The principal of operation is based on the relative change in the thermal conductivity of the gas passing across the detector filament as components elute from the column. Heat is lost continuously by the filament through the carrier gas to the cell wall of the detector.
Introduction 2 Safety Notes and Information Symbols HOT SURFACE The surface of the detector body may be hot while in operation (possibly in excess of 250°C). Observe caution. ATTENTION Refer to the manual. PROTECTIVE EARTH This internal connection provides protection against electric shock from mains voltages and should not be removed. Installation Category This equipment has been designed for installation category (overvoltage category) II, pollution degree 2.
Introduction 3 Components of the Detector Systems Components of the detector system are listed in Tables 1 and 2. Check the contents of the packages to verify that everything is present. Contact the factory if anything is missing or damaged. (NOTE: damaged shipments must remain with the original packaging for freight company inspection.
Introduction 4 Description of Controls and Connectors Controls and connectors are indicated in Figures 2 and 4. MAINS switch (rear panel) Controls mains (line) voltage to the controller unit. When this switch is on ( | ), the unit is operational except for the detector filaments (see next paragraph) and the detector heater will operate if connected. FILAMENT switch and indicator Controls power to the detector filaments; when the switch is on, current passes through the filaments.
Introduction 5 Figure 2: Front panel controls 400 350 ACTUAL TEMPERATURE IN °C 300 250 200 150 100 50 0 0 1 2 3 4 5 6 7 8 9 FILAMENT TEMPERATURE KNOB SETTING Figure 3: Actual filament temperature vs.
Introduction 6 MAINS POWER connector For connection to 115/230 VAC source. CHART OUTPUT connector Normally connected to a strip chart recorder. This output has an attenuated range of 0-1 volt and 0 - 10 volts, with the signal scaled by the attenuation factor set on the front panel. The output also has an internal signal reference (-) at zero volts. For best noise performance, the shield (earth) and signal reference (-) should not be connected together.
7 System Requirements Components Not Included with the Detector System • Carrier gas (99.
System Requirements 8 However, while nitrogen as a carrier yields excellent response to hydrogen, the response to oxygen and carbon dioxide is diminished compared to the levels that could be achieved with helium or hydrogen. Argon would yield poor response to carbon dioxide and water, but would be adequate for other components. There is no absolute “best choice” of carrier gas.
9 Installation The detector is usually mounted on top of the GC column oven. The power cord for the controller is 1.8 m (6') long; the detector cable and the signal output cables (attenuated and unattenuated) are 1.2 m (4') long. General Precautions • Do not turn the unit on until the carrier gas is flowing through the detector. • Do not shut off or disconnect the carrier gas when the detector is hot, even if the unit is turned off.
Installation 10 Gas Connections Remember these three points discussed earlier: (1) all surfaces that contact the gas stream must be glass or stainless steel; (2) do not use copper tubing or brass fittings; and (3) all tubes must be thoroughly cleaned and baked before use. The installation instructions below assume that the detector carrier will be supplied from a nearby cylinder. If your installation is different, you may need to modify the instructions appropriately. Consult the VICI catalog or vici.
Installation 11 Installing and Purging the Gas Regulator 1. Make sure the on/off valve on the helium cylinder is completely closed. Screw the CGA fitting nut of the regulator into the helium cylinder. Go beyond finger-tight, but do not tighten the nut all the way – some leakage is required for the purging operation. 2. Turn the output pressure regulating knob completely counterclockwise. 3. Open the cylinder on/off valve slightly and quickly close it again. 4.
Installation 12 Column Connection To prevent detector contamination, we strongly recommend disconnecting the column from the detector during column bakeout procedures. Referenced mode In the referenced mode, the column is connected to the Channel A inlet, and the carrier gas stream is split and used as a reference in channel B. The gas flow rate from both channels must be the same (flow balanced). This mode of operation provides the best baseline stability and the least background noise.
Installation 13 Packed Columns with Swagelok®-type Female Nut The connection of these columns is similar to that for standard packed columns, but requires a union which adapts the female nut to the Valco fitting. EZU1 Used with 1/16" column EZRU21 Used with 1/8" column Capillary Columns Connection of these columns requires the use of the ZU1C with the appropriate fused silica adapter. For a .53 mm ID x .8 mm OD column, use the FSR1.8 supplied with the TCD.
Installation 14 2. Connect the data output(s). The A / B / A - B outputs are used with an integrator or PC-based data acquisition system; the chart output is for a strip chart recorder. Polarities and full scale range are indicated in the figure below. (Set the recorder/DAQ for the same voltage scale.) 3. Connect the main power cord. Valco Instruments Co. Inc. MAINS MODEL TCD2-C T2.0A 250V 115/230 175VA MAX.
Installation 15 Initial Power-Up Since the TCD is a concentration-dependent detector, the lower the flow rate through the detector, the higher the sensitivity. Column diameter will determine the optimum column flow rate. The microvolume TCD is designed for the lower flow rates typical for capillary columns, and achieves best sensitivity at rates below 10 ml/min. Since the filaments are maintained at constant temperature, the detector can be operated at extremely low flow rates (less than 0.
Installation 16 The test chromatogram accompanying your TCD was obtained under the following conditions: Sample: ~100 ppm blend in Helium balance Sample volume: 250 µl Column: 10' x 1/16" x 0.040" molecular sieve 5Å micropacked Column flow: 6 mL/min Reference flow: 6 mL/min Column temperature: 65°C Detector temperature: 100°C Filament temperature: 230°C (a setting of 5.0) Carrier gas: Helium Balancing the Channels using LCD Display The LCD display indicates the signal level from the recorder/chart output.
17 Troubleshooting Troubleshooting Chart Problem Possible Cause Refer to page: No signal Main or filament power switch off Filament temperature too low Fuse blown Output cable in the wrong connector 4 4 3 14 Signal reversed Signal wires reversed 14 Noisy signal Dirty system or leaking fittings Bad flow controller in system Cell/filament differential too small Filament damaged 7, 13, 19 15 15 2 Cannot zero the signal Recorder/Int.
Troubleshooting 18 Detector Fault Determination Electrical faults in the detector are most easily discovered by making resistance measurements between pins of the detector cable connector. The table below shows the pin numbering and connections for the detector cable (view into pins). Nominal resistance values (in ohms) at 25°C are shown. Unshaded boxed without numbers represent open circuits, and should in no case be blow 1 MΩ. Resistance values given should be within ±10% of the nominal values.
19 Maintenance Cleaning the Enclosure The exterior of the instrument should be cleaned regularly with a dusting brush. If necessary, the casing can be cleaned with a moistened cloth (99% water + 1% mild detergent). Spirit or petroleum ether can be used to remove greasy dirt. Any other cleaning agents can attack the plastic and painted surfaces. Under no circumstances should the cleaning fluid get into the instrument. Petroleum ether is flammable, and care should be taken in its use.
20 Warranty This Limited Warranty gives the Buyer specific legal rights, and a Buyer may also have other rights that vary from state to state. For a period of 365 calendar days from the date of shipment, Valco Instruments Company, Inc. (hereinafter Seller) warrants the goods to be free from defect in material and workmanship to the original purchaser.
21 Detector Performance Log Detector Model: Date TCD2 Operator Serial Number: Comments Date of purchase: Filament Detector Noise temp temp level (°C) (°C) Initial power-up (IPU) — IPU, detector to analysis temp — — Ambient — IPU, column installed IPU, column to analysis temp 100 Sample — — Detector flow A B
