A Differential Pressure Transducer That Ensures Fresh Airflow for Animal Cages

Keeping a clean and steady flow of air is extremely important in any enclosed environment. This is particularly true in a laboratory environment, where isolation and control of all elements and potential containments is essential. The animal caging systems discussed here were designed with those requirements in mind.

The Air Flow Technology (AFT) department of Allentown Caging Equipment (Allentown, NJ) is responsible for designing and developing a range of airflow-related products. For over 35 years, the company has been providing the biomedical research community with the most technologically advanced animal housing systems. Recently, the AFT department designed two products that offer improved ventilation of the company’s P/NC Positive/Negative Control Systems.

The P/NC system is an individually ventilated caging system with 60–160 cages designed to hold up to 800 mice, rats, guinea pigs, or other rodents. These safe and flexible environments are HEPA filtered, and can switch from positive to negative pressure at the press of a button, providing a safe environment for both the animals and laboratory personnel. These caging systems use microprocessor-controlled supply and exhaust blowers to provide the required number of controlled air changes per hour. To help ensure that the systems maintain a stable airflow, and to measure airflow both into and out of the cages, the AFT team used differential pressure transducers from Setra Systems Inc. (Boxborough, MA).

Handling the pressure

Figure 1 - The model 265 series of pressure transducers, a primary ingredient in the SE6000 Smart Exhaust Pak. The Pak extracts dirty air from the animal cages and HEPA filters the air before it returns to the cage.

Setra Systems offers more than 35 years of experience in the design and manufacture of pressure measurement systems for HVAC control. The model 265 differential pressure transducer (Figure 1) was a perfect fit for the AFT team’s airflow monitoring and control needs. The team selected the model 265, which is offered with ±0.25% accuracy (±0.4% optional and ±1% standard) in pressure ranges from ±0.1 to 100 in. of water column (WC). The model 265 provided the stability and high-level output that is required for high-efficiency air control systems.

The team considered less expensive options, but it was determined that the model 265 offered the high level of quality and accuracy Allentown Caging Equipment was looking for, specifically, accuracy in low-range applications. The instrument is a key component in the SE6100 Smart Exhaust Pak (Allentown Caging Equipment), the unit that is responsible for extracting air from the P/NC system’s animal cages. Custom-made for the P/NC system, the Smart Exhaust Pak features a microprocessor control board and feedback control technology to automatically adjust the blower speed and maintain the desired 15–50 cfm airflow as the HEPA filters begin to load. The model 265 pressure transducer allows the SE6100 to constantly monitor the flow of evacuating air—air that is replete with airborne particulates such as dander, bedding, and dust, as well as potential pathogens.

Allentown Caging Equipment uses mass flow sensor technology with a hot tip anemometer on its supply blower to control the fan motor and adjust for HEPA filter loading. The problem with using this method for an exhaust system is that the delicate sensor would be exposed to airborne particles. This mass flow technology would require constant cleaning. The particles would block the hot tip and cause the unit to go out of calibration and greatly detract from accuracy. The model 265 allows the company to measure and monitor the pressure, permitting the Smart Exhaust Pak to precisely measure and control the P/NC system’s airflow accurately, without the added costs of recalibration and additional maintenance.

Easy detection

Figure 2 - The Range Finder Rack Flow and Cage Flow Detectors provide simple, fast verification regarding acceptable airflow and air quality into animal cages. The model 265 pressure transducer provides the positive and negative pressure sensing that is required in such a system to ensure a high-efficiency air control system.

The model 265 is also central to the company’s Range Finder Rack Flow and Cage Flow Detectors (Figure 2), which are also used with the P/NC cage rack. The Range Finder Rack Flow Detector provides supply or exhaust air confirmation for an entire ventilated rack, while the Cage Flow Detector provides cage-level airflow confirmation as low as 0.15 cfm from cage to cage. The Range Finder products can be used while the ventilated rack is in service and fully populated, with no disruption to its inhabitants. Both of these detectors utilize Setra’s transducer technology to provide simple, easy-to-read analogue output and accurate pressure measurement. The model 265 transducers used in Range Finders measure low differential pressures from 0 to ±0.25 in. WC with a high-level output accurate to ±0.4% of full scale.

Allentown Caging Equipment’s customers need to know how much fresh air their animals are getting in real time. The Range Finder products with the Setra technology provide the simple and fast verification the company’s customers require. Verification is easy: a green light for airflow that is within the selected range (typically ±10%) and a red light signifying unacceptable airflow falling outside that range. Within seconds, the Range Finder solutions allow users to spot check every rack and every duct connection in the cage system.

By taking advantage of the model 265’s precise pressure measurement and tight tolerances, the Allentown Caging AFT team was able to produce easy-to-operate air measurement and control solutions that do not require an abundance of extra parts. As a result, the P/NC system’s environmentally sound cage equipment ensures that the system’s residents are not the only ones who can breathe easier.

Mr. Troyer is HVAC Product Marketing Manager, Setra Systems Inc., 159 Swanson Rd., Boxborough, MA, U.S.A.; tel.: 978-266-3607; fax: 978-264-0292; e-mail: [email protected].

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