LEVEL SENSOR TECHNOLOGY: Electrolab Model 2100 Digital Level Sensor (DLS) vs. GWR
In the oilfield, automation engineers and technicians typically fall into one of two camps for level measurement: diehard Guided Wave Radar (GWR) fans or float-based sensor fans. The reasons are varied and the choice of a particular manufacturer is made based on a variety of factors. This blog discusses a few of the most common questions asked when deciding which type of level sensor to choose.
Q: What are the biggest differences between a typical guided wave radar sensor and an Electrolab Model 2100 DLS?
A: Principle of Measurement – Inferred Measurement vs. Direct Measurement
The fairest comparison is to start with the measurement principal. A guided wave radar sensor uses an inferred measurement, based on microwave technology. The GWR antenna sends a low energy microwave pulse down a probe (or cable) to the surface of the fluid to be measured. When the pulse hits the fluid a significant amount of energy reflects up to the antenna. GWR uses the speed of response from the pulse sent and pulse received to calculate the level measurement. This measurement results from determining the curve of the signal over the length of the cable. However, the speed of this signal coming back to the antenna is often affected by other factors, which industry refers to “false echoes.” For example, the dielectric constant of the material around the probe or cable can produce “noise” or an unwanted signal. See our April blog topic “Electrolab Level Sensors Eliminate the Issue of False Echoes.”
The Electrolab Model 2100 DLS offers direct measurement of the fluid in a tank. The floats on the sensor reside directly in the liquid. Magnets in the floats activate reed switches inside the sensor to determine the level of the fluid within a specified resolution (1/8”, ¼” or ½”). The sensor measures level direction without any interference or noise and without the need for any extrapolation or calculation.
In the oil field, simplicity is king. Pumping and storage of fluids can be unpredictable. Emulsion, foam, condensation are frequently present in tanks. Every tank has some sediment on the bottom. GWR antennas pick all of pulses from all these materials. These “extra” signals must be filtered out. As soon as the sensor is calibrated for the existing environmental conditions, something changes: the weather, the water content in the produced fluid, fluid chemistry, etc. Every time the environment changes, technicians must calibrate and adjust the sensor to filter out unwanted signals. This repetition requires constant oversight, time and labor. If there were any savings on the initial purchase of the equipment, the ongoing maintenance and calibration cycles quickly exceed this amount.
Direct measurement is simple and reliable. Floats remain buoyant in the fluid you are measuring, ensuring accurate level measurement. Whether it is -40oF or 140oF, the floats float, the magnets energize switches, and the measurement continues without ongoing calibration or maintenance.
The principle of direct in-fluid measurement is particularly pertinent in the separator environment. GWR sensors frequently struggle finding the interface level in the separator environment. Surface fouling, contaminants, tank flow rates and other environmental conditions complicate this challenge. Electrolab’s Model 2100 DLS works extremely well in this environment. See our May blog “Electrolab Model 2100 Digital Level Sensor Ideal for Separators” to learn more.
Q: But don’t Floats stick?
A: Not on an Electrolab Model 2100 DLS
It’s too easy to say “floats stick.” This is not a universal truth. There are however, two very important points to consider:
- First, unless a metal surface is treated with a chemistry such as e9 Treatments, paraffin sticks to anything metal, including guided wave radar probes (cables). All external metal surfaces of Electrolab Model 2100 DLS are factory treated with e9 Pro Performance Metal Treatment. This treatment changes the chemistry of the metal surface, reducing build up and allowing floats to move freely in even the harshest conditions. The Model 2100 DLS is the only level sensor on the market with this surface treatment and due to patent protections is the only level sensor in the US oil & gas market that can incorporate this treatment.
- Second, GWR sensors typically offer Teflon or a variation of it as an option. This option sells for up to $300 on top of the cost of the sensor. However, Teflon is a coating, not a surface treatment. It creates a new surface that can and will flake off particularly when the cable is cut to length in the field. This leaves an exposed cable, open to corrosion, exposed to areas prime for scale and paraffin build up.
Q: What about Maintenance?
A: The Electrolab Model 2100 DLS requires little to no ongoing maintenance.
Maintaining a GWR has two components, the physical and signal. Regarding the prior discussion about paraffin, it is common practice for technicians to pull the guided wave radar cable periodically to wipe off paraffin and other build up. This requires a technician on top of the tank, oftentimes under air, presenting an obvious safety hazard.
Next is the signal. As we discussed, technicians must periodically adjust the sensor signal to tune out false echoes. This process requires a laptop, special custom software, and trained technicians. Companies invest heavily in training and retraining technicians on the process of reading the signal curve and filtering out false echoes.
The Model 2100 DLS is different. Sensors treated with e9 Pro Performance should not show paraffin buildup. Therefore, there should be no reason to pull the sensor just to remove paraffin buildup.
The signal never changes. Temperature does not affect the position of the switches, the magnetic field or the floats. Floats find the oil level and interface level regardless of water content, foam, condensate or other foreign liquid in the tank. The bottom line is that Model 2100 DLS can and should be put into a tank and let run for years without maintenance.
Q: What about Installation?
A: Different types of level sensors have different installation requirements.
Many installers prefer GWR sensors because they are easier to install, the cable or probe can be cut in the field to the required length or the sensor itself just appears sleeker. While there may be some merit in these preferences, these same features can contribute to increased maintenance over the life of the sensor, due to factors previously discussed in this article: paraffin buildup requiring frequent maintenance, ongoing need for adjustment and calibration, and exposed cuts subject to corrosion.
The Model 2100 comes in a rigid and flexible design. While the rigid sensor does require more effort to install, it requires only one-time calibration and then it is set to operate for the long-haul. The rigid sensor is designed for turbulent and high flow tanks where a flexible sensor might not be appropriate. Rigid sensor come with either stainless steel or fiberglass tubes depending on the nature of the fluid in the tank. High H2S, high-corrosive environments and SWD tanks are better suited to the fiberglass option. The flexible sensor is easier to install and is reliable in many types of environments.