Category Archives: medical


Anesthesia Delivery Systems

One method of administering anesthesia to surgical patients on the operating table is via a vapor delivery system. In this method the anesthesia is poured into a vaporizer as a liquid
and medical grade oxygen piped to the vaporizer as well. A heater turns the liquid anesthesia to a vapor so that it can be integrated into the patient’s breathing mixture. The purpose of the vaporizer is to deliver the exact mix of oxygen and anesthesia, as called for by the anesthesiologist in the operating room. This is critical application involving human life. The Validyne P398 OEM pressure transducer is used in one such vaporizer in the sub-system that controls the mix of anesthetic vapor and oxygen to the patient by sensing the difference in flow rate between the two gases. When there are correct amounts of vapor and oxygen in the mix, the difference in the pressure drop due to their respective flows is zero as reported by the P398 pressure transducer. The sensitivity of the P398 pressure transducer to low pressures and its high reliability are the main features that have made this product successful in this challenging application. The P398 pressure transducer is used specifically in vapor anesthesia systems.

Sensing Diaphragm

Tips on Storing Validyne Sensor Diaphragms

The diaphragm or sensor membrane is the heart of a Validyne transducer. To increase the lifespan of replacement diaphragms follow these best practices to store and maintain your units.

Diaphragm discoloration may occur overtime due to the relative humidity while in storage.   The discoloration does not have any negative effect on the diaphragms performance unless very aggressive oxidation has taken place, but it is important to keep Validyne diaphragms in a non humid environment. The simplest way to achieve this is to insert the diaphragms into a small plastic zip bag to keep the units dry until ready to use. You may also store the diaphragms with a silica gel desiccant or similar product, but be sure that your absorption material is not touching the diaphragms during storage.

If you do notice discoloration, the diaphragms may be cleaned with IS formulated cleaning solution inside an ultrasonic cleaner for 10 minutes. Next, rinse with DI water and finally with alcohol to neutralize the water. Dry the diaphragms with clean shop air and store as per instructed above. This process will not eliminate all of the diaphragms discoloration but, as explained above, the discoloration will not affect the diaphragm performance. Do not try to sand blast or use sand paper to remove stains since this process will affect the diaphragm performance (creating poor linearity and hysteresis).

If you are still experiencing issues, we make diaphragms coated with Teflon, gold and nickel plating that will protect the diaphragm from discoloration over time. This will also safeguard the diaphragm against more corrosive solutions such as water, brine, acids, and heavy bases. If you have any questions of which diaphragm works best with your material, please don’t hesitate to ask the sales department at Validyne.

Measuring Pressure Drop Across Protective Mask

measuring pressure dropFace masks are often the first line of defense against the spread of infection or damaging particles. A properly designed face mask will stop dangerous materials, but allow normal air flow for breathing. The mask material must be woven tightly enough to trap unwanted particles, but the pressure drop through the mask should be low enough so that breathing effort is normal. Testing protective masks requires measuring pressure drops which equal to just a few millimeters of water.

measuring pressure dropThe Validyne DP103 differential pressure transducer is available in full scale pressure ranges as low as 3.5 mm H2O. This pressure transducer was recently used to measure the pressure drop through prototype face masks that were on the order of 5 to 10 mm H2O. The pressure drop was to be recorded at different flow rates and this required a pc based data acquisition system  for the output of the DP103.

Basics of Pneumotach Flow Measurement

Pulmonary function testing is a medical diagnostic procedure that measures how much air you are breathing and how fast. These parameters are measured with a device known as a pneumotach. A pneumotach is essentially a light screen that is inserted in the airflow. The pneumotach creates a known pressure drop that is directly proportional to the air velocity. A pneumotach is connected to an air tube that allows the patient to breath freely. As the air moves in and out of the patient’s lungs the flow of the air creates a small drop in pressure across the pneumotach screen. A sensitive pressure transducer, like the Validyne DP45, is connected to the pressure taps of the pneumotach and produces an analog signal proportional to the flow rate. This signal is integrated to volume so that the amount of air and its flow rate into the lungs is known at each instant in the inspiration/expiration cycle. The pneumotach typically is equipped with a heater to keep condensation from forming on the pneumotach screen. A typical system is shown below.

Pneumotach Flow Measurement

Pneumotach Flow Measurement

Typical System:
The key to quantifying these measurements is knowing the relationship between flow rate and pressure drop across the pneumotach screen. Pneumotachs come in several sizes, depending on the patient size. A pneumotach used for measuring lung capacity of an adult athelete will be different than a pneumotach designed to measure breathing in premature infants. It is important, of course, to select the correct pneumotach size for the intended measurement. In any case, every pneumotach style will have a chart showing the relationship between air flow and pressure drop. An example is shown below.

Pressure Differential vs Back Pressure






The Validyne transducer measures differential pressure so the conversion of the pressure signal to flow is a matter of some simple algebra. For example, the pneumotach chart above states that the pressure drop across the pneumotach will be 17 mm H2O at a flow rate of 800 L/Min. The Validyne DP45 in its most sensitive range, is calibrated such that 20 mm H2O = 10 Vdc signal output. Since the pneumotach flow/pressure curve and the DP45 transducer are nominally linear, we can easily convert the output signal of the DP45 demodulator from volts to L/Min, as follows:

800 L/Min = 17 mm H2O and the signal from the DP45 demodulator is 10 * (17/20) = 8.5 Vdc at this flow rate. Therefore flow in L/Min = 800/8.5 = 94.12 * Vdc So the data acquisition system simply needs to multiply the DP45 output signal in volts by 94.12 to have the flow rate in L/Min.

Welcome to the Validyne Engineering Blog

This is the new Validyne Blog. The idea is to post useful information about using Validyne products and describe the applications of our pressure sensors.

This is also a place for you to give us feedback. Please feel free to comment on this blog – to ask a question or to tell us about how you use our transducers.