Tag Archives: DAQ

Car Door Seal Testing

Car Door SealWhen 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.

Reducing Glove Box Filter Costs

Glove Box Filter

Handling radioactive materials must be done in glove box. A glove box is a clear plastic enclosure with rubber gloves attached to the sides so that an operator can handle material inside the glove box, but air and radioactive dust are not allowed to escape. The air pressure inside the glove box must be controlled so that it is always less than the ambient atmosphere. A series of risers, ducts, fans and filters connected to the glove box keeps the pressure inside the glove box lower than the outside atmosphere so that no dust can escape.

If the airflow velocity up the riser from the glove box is too high, radioactive dust is carried into the exhaust system, and these particles are trapped by a series of special filters. When a filter needs to be changed, it is very expensive to dispose of the dirty filter because it is charged with radioactive dust and dirt. The key to reducing filter disposal costs is to limit the exhaust airflow velocity so that dust is not carried out of the glove box and into the filters, while at the same time insuring that the pressure inside the glove box is always less than the ambient atmosphere.

Measurement of the air velocity in the glove box risers is accomplished with a pitot tube and a sensitive differential pressure transducer. As air velocity increases, the differential pressure across the pitot tube increases. The very low velocity needed to exhaust air from the glove box, without raising dust translates into a very low pressure drop across the pitot tube. This pressure drop is as little as 0.02 In H2O under normal operating conditions. A very sensitive differential pressure sensor, combined with a high level DC signal output, is needed to provide the air velocity signal to the system controller.

A special version of the Validyne P532 provides the low pressure measurement required for such a control system and these are used at a major North American nuclear fuel rod processing facility.

Validyne introduces World’s first Automotive Cabin Pressure Checker


Highly Configurable, Very Low Differential Pressure Transducer System Measures and Records Cabin Pressure Fluctuations

Northridge, CA – April 29, 2015 – Validyne Engineering introduces the World’s first Automotive (Transportation) Dynamic Cabin Pressure Checker.

VPAS, Vehicle Pressure Acquisition System, is used to detect rapid pressure changes due to: Sun roof opening, side or rear window openings, windshield leak detection, and HVAC testing and verification.

According to Richard Ganz, Validyne’s Director of Business Development “A new wave of automation has recently been ushered into the Auto Industry: from self-parking to self driving systems such as the Tesla Model S and the Mercedes F 015. Validyne is committed to support the sensors and related systems that support a safe and comfortable driving experience.”

A World Leader in Variable Reluctance Technology (VRT) since 1968, Validyne has a rich history of providing standard and custom solutions to the Auto industry.  In the Mid 90’s, Validyne designed to General Motors (GMC) specifications, a Vehicle Standard Thermal Instrument. Commercially available and in use today as VDAS, it is an in-vehicle data acquisition system (DAQ).

Hyundai Motor Company (HMC) has announced its desire to move forward and procure a VPAS production system for use as a standard efficiency test and check across all Hyundai and Kia vehicles.

A portable, vehicle-powered VPAS is designed to measure, record and display sensor readings from 1 to 16 channels. The VPAS software is integrated for PC or iPad and is used to measure vehicle cabin pressures under various conditions.  A unique reference to atmosphere can be enabled at any time.

The VPAS system is comprised of a Validyne USB2250 sensor interface with on-board signal conditioning for VRT or any other manufacturer’s pressure sensor.  Validyne model DP103 pressure sensors – included on VPAS – can measure full scale ranges as low as +/-0.10 In H2O and up to +/-55 In H2O.

Pressure readings are available for continuous display and graphing on a laptop PC or iPad via USB interface integral to the VPAS.  The transducer readings are calibrated for In H2O and the data is recorded to a .csv file and displayed graphically in real time.


Validyne Engineering Inc., headquartered in Northridge, Calif., has a diverse customer base that ranges from automotive and engine manufacturers, to research and development labs, to aerospace companies. For more information on Validyne or to find out more about the new VPAS Pressure System, please visit www.validyne.com, send us an e-mail at sales@validyne.com, or reach us by calling (818) 886-2057.


Established in 1967, Hyundai Motor Company is committed to becoming a lifetime partner in automobiles and beyond. The company, which leads the Hyundai Motor Group, an innovative business structure capable of circulating resources from molten iron to finished cars, offers top-quality best-sellers such as Elantra, Sonata and Genesis. Hyundai Motor has seven manufacturing bases and seven design & technical centers outside of South Korea and in 2013, sold 4.73 million vehicles globally. With almost 100,000 employees worldwide, Hyundai Motor continues to enhance its product line-up with localized models and strives to strengthen its leadership in clean technology, starting with the world’s first mass-produced hydrogen-powered vehicle, ix35 Fuel Cell. More information about Hyundai Motor and its products can be found at: http://worldwide.hyundai.com or http://www.hyundaiglobalnews.comm


Interfacing 4-20 mA Current Loops to the USB2250

Many pressure transducers and other field instruments use the two-wire 4-20 mA current loop for both power and signal. The 4-20 mA current loop is economical to install, using the same two wires for power and signal. It is also ideal for sending a signal over long distances – up to a mile or more – with high resistance to noise. Most data acquisition devices, however, are configured to accept voltage signals. This application note will describe how to interface a standard two-wire 4-20 mA current loop to the USB2250 sensor interface.

A typical 4-20 mA transmitter receives power from an external power supply. The power supply must be able to provide enough voltage and current to power the transmitter under all operating conditions. The transmitter will require some voltage just to produce a signal and the power supply must provide this plus any power needed to overcome any resistances placed in the current loop. The maximum amount of current required by the transmitter will be at least 20 mA, but it is best to select a power supply that will provide for 25 or 30 mA through the loop to allow for over-range indication by the transmitter.

To interface to a data acquisition device such as the USB2250 a resistor is placed in the loop and the voltage drop across the resistor will be connected to the USB2250 as a single-ended voltage input. To see how this works, assume the following conditions:

Minimum voltage required by the transmitter = 12 Vdc
Maximum loop current = 25 mA
Interface Resistor = 250 Ohms
Wire or other miscellaneous resistances in the loop = 20 Ohms

To calculate the voltage required for the power supply, we add up the voltage drops in the loop:

12 Vdc for the transmitter
Voltage drop through the wire = 0.025 * 20 = 0.5 Vdc
Voltage drop through the interface resistor = 0.025 * 250 = 6.25 Vdc

Adding these voltage drops together, the minimum voltage provided by the power supply must be 12 + 0.5 + 6.25 = 18.75 Vdc to push 25 mA through all the resistances in the loop. For a single loop the power supply will need to be rated for at least 18.75 * 0.25 = 0.47 W, but typically a single power supply will power many loops before wattage ratings become an issue.  We can use a 24 Vdc power supply – just as long as it is greater than 18.75 Vdc.

The diagram below shows how the current loop is interfaced to the USB2250 terminal block. Note that the power return is common to the USB2250 signal ground. The voltage drop across the resistor is 1 Vdc when the signal is 4 mA and 5 Vdc when the signal is 20 mA, being proportional in between.

4-20 mA USB2250

USB2250 scale and offset factors in Easy Sense software are used to convert the 1 to 5 Vdc input into engineering units. If, for example, the 4-20 mA signal is for a 100 psig pressure transducer, then at an input of 1 Vdc the pressure is 0 psig and at 5 Vdc the pressure is 100 psig.

The algebra is simplified by first determining the scale factor = change in pressure/change in voltage = 100/4 = 25.

Multiply the scale factor by -1 to obtain the offset factor: 25 * -1 = -25.

Check by determining the readings at each end point:

At 1 Vdc the reading will be R = (25 * 1) -25 = 0 psig

At 5 Vdc the reading R = (25 * 5) -25 = 100 psig

The USB2250 will read the input from the current loop and provide readings in psig or any other engineering units.