A good approach is to first compare the hydrocarbon analyzer specification sheets published by the various manufacturers. Each manufacturer is attempting to convey similar information and each should be familiar with competitive offerings. Write down questions that you will want to have answered and keep in mind how you will be using the equipment.

Give the manufacturer's representative as much information as you can about your application and also what other instruments you are considering using. A reputable manufacturer will tell you if their equipment is unsuitable for your requirements, or what other equipment must be purchased with it to make it work properly in your application. You may need items like heated probes, sample lines, multipoint selectors, pre-filters or external equipment controllers and it may be advantageous to purchase them working together.

Often one manufacturer will feel that some performance criteria are more important to the potential end user than others. Targeted applications often require some reshuffling of engineering priorities and the enhancement of some instrument characteristics. Manufacturers may offer several models in response to this fact.

For instance, the testing of automotive engines requires an extremely fast response time in order to obtain the most useful data. Diesel engine testing requires enhanced protection from particulates in addition to fast response. Additional equipment like pre-filters and fast multipoint sequencers may be useful to this application.

Response time is also a primary consideration in certain process monitoring applications where the hydrocarbon analyzer is used as the primary input to a control loop. Usually, response time is given as T-90 or T-5 to T95. That is the time it takes for the instrument to respond to 90% of final value, or from 5% to 95% of final value following a step change at the analyzer's sample inlet.

In process monitoring applications, built-in bi-directional serial communications, descriptive alarms and relay outputs also become an important part of process control and safety considerations. You would not want to use an older style analog instrument as the control loop primary input.

In some applications, the sampling matrix is variable, or partially unknown. The oxygen content or constituent species may change considerably during the course of testing, or from one source to another. Here it is important that the hydrocarbon monitor FID be as free as possible from oxygen effect and that the instrument's relative response to various hydrocarbon species is predictable or well characterized.

The oxygen effect is sometimes called "Oxygen Synergism". This is somewhat of a misnomer as it is actually the reduction in response caused by the partial oxidation of the hydrocarbon species by oxygen in the sample gas prior to analysis. The greater the oxygen content, the more pronounced the effect can be on the instrument response. Fortunately, it is easily characterized as a logrithmic curve; carefully controlling the fuel and combustion air flows allows this effect to be largely minimized. In general, the detector fuel and air flows are adjusted to calibrate the instrument at two points on the curve using calibration gasses in backgrounds of 0% oxygen and 21% oxygen. For all gas samples with oxygen contents that fall within these two values, the data should be valid. A maximum deviation of 1%-2% of the sample concentration is normal for a high quality instrument.

Relative response in a FID to various hydrocarbon species is a function of carbon content, how these carbon atoms are arranged in the molecule and the presence and arrangement of other groups in the molecule. Response factors express the variance from the carbon count and are usually given in terms of a reference species such as propane or methane or in ppm carbon.

Manufacturers of hydrocarbon analyzers may publish analyzer data for some species tested under optimal conditions. If you are fortunate enough to have a copy of an early Beckman FID manual, it is an excellent resource for both oxygen effect and response factor derivations.

Equally important, is the instrument's calibration repeatability and drift characteristics. A hydrocarbon analyzer's response to calibration gas and zero baseline must not change significantly during the course of testing or between calibration cycles.

Apart from basic FID detector design, relative response, oxygen effect and calibration repeatability are functions of carefully controlled and consistent flows of fuel, combustion air and sample gas through the detector. The monitoring and verification of these parameters are an important part of the calibration audit trail. Instruments which time-stamp and record calibration adjustments are highly desirable in the documentation of calibration integrity.

 

Overall Quality Construction, Safety and Workmanship:

Look the equipment over for fit and finish. Small things matter like connectors, displays and controls. The equipment should be quiet. Noisy equipment is vibrating something loose. There should be no knife-sharp edges to cut an operator or installer.

The equipment you purchase should be well-engineered, safe and reliable. ISO 9001 certification of the manufacturer's facility is a good indicator of overall manufacturing system quality. The equipment should feature a CE, UL, CSA, VDE or similar certification for safety and conformance. Many manufacturers' designs are unable to achieve this due to poor design practices, construction methods, electrical safety and EMI issues. Incredibly, there are no government requirements for minimum safety and conformance of scientific equipment manufactured in or exported to the U.S. It is the purchaser's responsibility to determine the safety and suitability of the equipment. Play it safe with hydrogen-fueled instruments! Be sure that the equipment you select has been passed and certified by a major independent product testing lab and bears UL, CSA, or CE markings.

Calibration Integrity / Data Quality:

It is not possible to speak for other manufacturers on the following issues as they are somewhat broad and can get very detailed. Suffice it to say that we are confident that we lead all others on these points by a wide margin. Here are details of our approach to data quality and overall quality:

The Signal Instruments Model 3000HM's processor time and date-stamps the last calibration adjustment, displays the current calibration relative to the maximum allowable adjustment and rejects adjustments which indicate severe malfunction. Out of tolerance conditions are indicated on the calibration report and the last good calibration data is retained.

Parameters which affect the calibration (oven, detector, catalyst temperatures, reference & fuel pressures and sample & calibration gas flows) are all available simultaneously with continuous concentration data via the menu interface and as serial data. These parameters are continually monitored and flag a failure alarm if out of adjustment. Conditions that result in a failure alarm cause the equipment to automatically shutdown to a safe, standby condition. Upon correction of the alarm condition, the analyzer operaration may be immediately resumed.

Pressure regulators for fuel and reference are of a high accuracy, tool access type which cannot be adjusted inadvertently (during shipment or by knob-twisting) and do not require adjustment during calibrations or normal servicing. These settings are easily verified and adjusted to factory specifications by the operator.

Copies of original quality control checkout documents are included with the new monitor and maintained on file at K2BW Environmental Equipment Co. for operator assistance and electronic distribution.

The 3000HM heated hydrocarbon monitor's response is insensitive to a wide range of sampling pressure conditions and reaches full rated accuracy within one hour.

Temperature control circuits and display functions are designed to fail-safe, operate closed-loop under microprocessor control and are adjustable only within their normal operating bands. Actual flame temperature is monitored and available to the operator to assist in fault isolation.

The FID combustion air supply is completely internal to the analyzer, eliminating the need for external supplies of compressed hydrocarbon-free air. This unique design employs a true catalyst which eliminates all ambient hydrocarbon species (including methane). The internal combustion air supply may also be easily used for calibration zero gas (also allows verification of catalyst efficiency), eliminating the requirement for external supplies of compressed zero air. This standard internal feature alone saves the expense and complication of external combustion air and zero gas supplies.

Many of the sources of calibration and data error have been eliminated in the Model 3000HM and an excellent audit trail may be established using the instrument's status and alarm information along with concentration and process data.

Usability and Reliability:

The Model 3000HM has been designed to use the power of its microprocessor to make operation simple and safe. It's backlit LCD display and soft key operation allow new users to operate the instrument without continually referring to the manual. The user needs only to provide the instrument with fuel gas, apply electrical power and press the "sample" soft key. The instrument will perform all the necessary self checks. When the detector assembly is up to operating temperature (about 15 minutes), the instrument lights itself, sampling from the internal zero air supply. Upon reaching an acceptable air catalyst and flame temperature, the sample path opens. All of this occurs automatically, without further operator intervention.

Calibration of zero and span points may be programmed to initiate and adjust automatically or can be performed manually. Two fully programmable (high or low going) level alarms allow the analyzer to trigger events or alert operators via relay outputs.

The model 3000HM's electro mechanical design is inherently reliable. A 0.4 micron sintered Teflon® filter element offers superior particle exclusion to other types, is cleanable and does not corrode or shed fibers into the instrument. The sample filter housing and all components in contact with the gas sample are connected in a solid 316 stainless steel block which is actively heated to 193 C. This drastically reduces the number of tubing connections required and eliminates the likelihood of leaking tube fittings. The Model 3000HM also contains fewer moving parts while achieving greater function than competitive equipment; it has one pump assembly, one cooling fan and four solenoid valve operators. All electronic printed circuit boards are mechanically secured in a standard card cage with locking card retainer. The compact, 3RU formed aluminum case is light and strong and suitable for 19" rack mounting or bench top use.

Due to a reliable, automatic ignition system, the igniter is unlikely to burn out. It may be replaced without opening the heated detector assembly during servicing.

Strength of Warranty:

The Signal Instrument Model 3000HM's warranty is two full years against defect in materials and workmanship. We want you to be happy with your decision to purchase our instruments so we will work with you on applications and service for as long as you own them. Initially, we will do our best to equip you for your application with the proper sampling accessories, heated line and spares appropriate for your needs. Then, for a full two years we will repair or replace (at our option, of course) any equipment which does not operate in conformance with the new equipment specification due to a manufacturing defect. And we'll make every effort to do it within three work days. We will even perform routine cleaning and adjustment for you free of charge. Just pay for shipping. After that, expect unlimited free applications engineering, troubleshooting assistance and all parts and major subassemblies kept in stock for immediate delivery (should you prefer to maintain it yourself). And if you have a truly major problem, we offer fixed-cost rental instruments while yours is in for repairs.

Price:

The Model 3000HM is actually less expensive to own and operate than other heated total hydrocarbon analyzers. While some other manufacturer's instruments may sometimes be priced lower for the basic instrument, these invariably require the purchase of additional equipment to achieve similar performance to the 3000HM. External heated pumps, supplies of combustion air or zero gas cylinders may need to be purchased separately. Remote control, alarms, auto-ranging and automatic lighting are usually only available in other manufacturer's equipment as options at additional cost. Simultaneous availability of voltage and isolated 4-20 mA current outputs and bi-directional RS-232 (which allows data logging on a standard PC without special A/D converter boards, etc.) are usually unavailable, or special order options. The 3000HM has all of this as standard as well as the excellent paged menu user interface. Our 2-year warranty and free preventive maintenance offer alone saves thousands on a purchase over other manufacturers' equipment.