The most popular Validyne pressure transducers are the P55/P61/P365 series. These all include a pressure sensor, carrier demodulator electronics package, a high level output signal, temperature and linearity correction as well as a compact form factor. There are applications, however, where a better solution might be to separate the pressure sensor from the electronics, with the two connected by a cable. This article describes when this approach makes the most sense.
Validyne offers the sensors and electronics package from the P55/P61 available as stand-alone components. The DP15 series of pressure sensors is identical to that used in the P55 and P61, while the DP360 and DP363 are high pressure variants the same as used in the P365 and P368. The CD16 standard analog output electronics or the CD17 USB-based electronics can be used with any of these sensors, and standard cables are available in a variety of different lengths to connect the two.
When should a sensor be separated from the electronics? The biggest reason to do this is to allow convenient re-ranging of the pressure sensor. The full scale pressure range of Validyne sensors can be changed by replacing the sensing diaphragm. There are 23 different full scale ranges available for the DP15, for example, and these run from a few inches of water to 3200 psi. Changing the diaphragm is straightforward; the connector and four body bolts must be removed to gain access to the sensing diaphragm, and the DP15 sensor makes this easy, requiring just a torque wrench and a vise. With a little practice, the diaphragm in a DP15 can be replaced and re-calibrated with the CD16 or CD17 electronics in about 20 minutes. The DP360 and DP363 high pressure sensors are similar in construction and also lend themselves to straightforward diaphragm replacement. Frequent re-ranging of the full scale of a Validyne transducer is common in laboratory situations where pressure measurements vary widely from day to day. Test labs and university labs are typical places where a separate sensor and electronics package are used to best advantage.
Another reason for separating the pressure sensor from the electronics is to conserve space or limit the weight at the measurement point. In tight locations, such as aircraft compartments or in submersible vehicles, the pressure connection may be in a relatively inaccessible space and the smaller footprint of the DP15 sensor, might fit better than the full P55. If mass or weight is important, the sensor will be lighter than the full transducer and this will relieve any stress on the piping connections in areas where shock and vibration are a consideration.
It is important to realize that separating the sensor from the electronics will compromise the temperature correction as the temperature sensor is located on the electronics package and not at the pressure sensor. A pressure sensor such as a DP15 used with a remote electronics such as the CD16 will be most effective in applications having a stable temperature environment.
When automobile doors are closed it is expected that the sealing surfaces around the edges of the door will contact the frame properly so that the passenger cabin is weatherproof and the inside protected from rain and water. With all the different styles of doors, frames and gasket materials each new model must be tested to verify that the sealing system is effective.
One way to test the seal is to measure the pressure rise inside the passenger cabin when the door is slammed shut. If the seal is effective there will be a brief rise in pressure. We have probably all experienced this – Volkswagen Beetles were notorious for the ear discomfort on door closings as they were deigned to be waterproof. So a balance between sealing effectiveness and comfort is desired and testing the pressure rise is one way to verify that the right combination of sealing materials is being used.
The measurement of a pressure rise in the passenger cabin requires a pressure transducer with sensitivity to low pressures and fast dynamic response. One automobile manufacturer uses the Validyne DP45 to measure pressure spikes on the order of 400 Pa having a duration of 10 mSec. The DP45 is available in full scale ranges as low as 220 Pa and has a flat dynamic response on the order of 60 Hz and can thus capture a transient whose rise time is 4 mSec.
The system is comprised of the following Validyne Parts:
The system cal is convenient because of the low pressures involved – we calibrate the system here prior to shipment. The customer attaches DC power (9 to 55 Vdc) to the connector and also the 0 to +5 Vdc signal wires to a high speed data acquisition system. The transducer has 1/8” female NPT ports and these are fitted with adapters by the customer to plastic tubing that is run to the inside of the automobile passenger cabin. The door is slammed several times at various velocities and the resultant pressure rises recorded. On this basis the gasket seal and firmness can be evaluated.
A carrier demodulator is the electronics that supports a variable reluctance pressure transducer. A carrier demodulator provides power to the transducer, provides calibration adjustments, receives the AC sensor signal and converts it to a useable output. What is the best carrier demodulator to use with your variable reluctance pressure transducer? The answer to that question depends on a number of factors.
Do you need a digital display in units of pressure? The CD23 provides an LED display which can be read from several feet away. The CD379 has a liquid crystal display. If a digital display is not needed, then the basic CD15 is probably sufficient.
Is 110 VAC available? Most Validyne carrier demodulators have a version that will run on standard 110 VAC power. For portable use, the CD379 is battery operated.
Looking for the lowest cost? The CD101 is a carrier demodulator circuit board. Add your own
enclosure and power supply for a custom solution.
The CD12 provides selectable gain settings up to 20 times higher than the standard demodulator. Combined with the zero suppression feature, the CD12 allows observation of small pressure variations that are riding on high static pressures.
If you have several transducers, then a multi-channel carrier demodulator such as the CD280 or MC1 system may be the most cost-effective carrier demodulation.
Do you want the signal to go into a PC? The CD17 is a USB interface for a single variable reluctance sensor. Up to 16 variable reluctance transducers can be supported by the UPC2100 PCI plug-in card or the USB2250 for USB interface to laptops. These card include complete carrier demodulation and A/D conversion as well as scale and offset factors for conversion into engineering units.
Find data sheets and instruction manuals on the products listed above www.validyne.com/carrier demodulator