Monthly Archives: October 2013

How the SU63 Speed Pickup Works

The SU63 Speed Pickup is a device designed to be used to sense the speed of turbochargers. A turbocharger rotates very fast – some 10,000 rpm or more, and standard sensing techniques for measuring the speed often fail in the conditions around the vehicle engine. This application note describes how the SU63 senses the very fast turbocharger rotation and how the signal is developed.

The SU63 is simply a coil of wire mounted on a flexible core and with a cable for making the signal connections. The SU63 is completely passive – it does not require power and generates a signal only in the presence of a moving magnetic field.

speed pickup

 

 

 

 

 

Here is how the SU63 develops its output signal:

speed pickup

 

 

 

 

 

A rotating permanent magnet, whose magnetic field sweeps through the SU63 coil will develop an induced emf that is expressed as a voltage. As the field sweeping the coil changes in strength and direction as a function of the magnet rotation, the voltage generated varies accordingly. The emf signal amplitude is proportional to the rate of change of the magnetic field in the coil.

In practice, a bolt head or nut on the moving shaft of the turbocharger is magnetized by leaving a strong permanent magnet attached to the part over night. The SU63 is placed such that the magnetic field from the part will sweep through the coil as the turbocharger rotates. The closer the coil is to the moving part – and the stronger the magnetic field – the better the voltage signal will be from the SU63.

Of course part of the time the magnetized part will be far enough away from the SU63 so that no signal is developed. But as the part passes by it will generate a kick in the coil that can be counted by electronics connected to the SU63. As the turbocharger spins faster, the signal will decrease in duration but increase in amplitude.

speed pickup

You can view the datasheet and product page of the SU63 here.

Selecting Accessories for the Recalibrating the P55 Pressure Transducer

Introduction:
The Validyne P55 pressure transducer has as its sensor a variable reluctance pressure sensor that can be re-ranged for different full scale pressure measurements. The sensor can be disassembled, a new sensing diaphragm installed and the unit re-calibrated to the new full scale pressure. Some 23 different full scale pressure diaphragms are available and this application note will describe how to select and order the parts needed to re-range the sensor and interface the signal to a PC.

Sensor Parts:
A typical P55 is shown below, with the external parts identified:

P55 Parts pressure transducer

 

 

 

 

First, remove the two Philips head screws holding the sensor to the P55 electronics housing. These are located on the underside of the housing. The wires from the sensor to the electronics are very short, so take care they do not break.

To disassemble a P55 sensor a torque wrench, T27 Torx socket and a vise are needed. The tools needed to disassemble the sensor are available from Validyne and are shown below:

torquewrench pressure transducer

 

 

 

 

 

The sensor can be disassembled by removing the four 10-32 Torx T27 body bolts. When disassembled, the sensor body pieces separate and the sensing diaphragm and o-rings are removed. These parts are shown below:

boltsorings pressure transducer

 

 

 

 

 

It is good practice to replace the body bolts and o-rings when changing the range of the P55. Various o-ring compounds are available (see ordering chart).

The sensing diaphragm may now be replaced with one of a different range. A typical sensing diaphragm is shown below:

diaphragm pressure transducer

 

 

 

 

 

To re-range a P55 sensor the full scale pressure must be known and the correct diaphragm part number ordered. The part number for a P55 diaphragm starts with 3- and is followed by a two-digit range code. The diaphragm in the photo above is p/n 3-22 and has a full scale range of 5.5 In H2O. The other available range codes for the P55 sensing diaphragm are shown in the chart below with their full scale pressures expressed in various engineering units.

P55Ranges pressure transducer

 

 

 

 

 

 

 

Re-assembly is simply the reverse of dis-assembly, taking care that the torque on the body bolts is 125 In-Lb. The vise is used to stabilize the sensor body during assembly and to allow the torque to be correctly transmitted to the body bolts.

Also be sure that the bleed screws are tightly seated – these use a 5/64” hex wrench, Validyne p/n K950-0781. The sensor is reattached to the housing using the two Phillips head screws.

Calibration Accessories:

The next step is to calibrate the P555 against a pressure standard. Validyne can supply model T140K calibrator kit that includes a pressure pump and reference standard – an example is shown below.

T140K pressure transducer

 

 

 

 

 

 

 

The T140K calibrator kit is available in six different versions covering the available DP15 full scale pressure ranges. To calibrate theP55 connect it the SI58 digital interface and have a voltmeter to observe the analog output signal of the P55 as it appears on the binding posts of the SI58. 

SI58 pressure transducer

 

 

 

 

 

The SI58 connects to any USB port on a PC and is supplied with software that allows changing the internal registers of the P55 to achieve an accurate calibration. Connect the re-ranged P55 to the SI58 and the SI58 to a PC. Connect a multimeter to the SI58 binding posts to observe the P55 output signal.  

P55Cal pressure transducer

 

 

 

 

Load the calibration software and follow the instructions for applying zero and full scale pressures using the T140K calibrator. The software will adjust the P55 microprocessor correction factors to produce an accurate calibration with the new sensing diaphragm.

The SI58 software also allows the user to compensate the P55 through temperatures. The temperature range can be selected by the user as applied by an environmental chamber. 

SI58 Software pressure transducer

 

Simple Manometer Calibrates Pressure Transducers

Introduction: A simple U-tube manometer made from easily obtained materials can be used to calibrate pressure transducers over the range of a few inches of water to a few psi. This application note describes how to construct a manometer and determine the accuracy that can be expected.  Items Needed:

  • 5 to 10 ft Clear Plastic Tubing
  • Ruler or Tape Measure
  • Water

Constructing the Manometer: A length of clear plastic tubing, formed into a U-tube and partially filled with water should be configured as shown below. Depending on the pressure you need to generate, the tubing should be a few inches to a few feet high. The limiting factor is likely to be the amount of vertical space available to form the water column. Connect one end of the manometer to the transducer pressure port (normally the + port). manometer pressure transducers               Secure the ruler or tape measure to the surface behind the U-tube. Raise or lower the free end of the tube to increase or decrease the fluid head applied to the sensor.  Note that the sensor need not be filled with liquid; the air inside the transducer has no place to go and will compress until it is at the same pressure as the fluid column. Determine the applied water column head by measuring the distance between the fluid level in each leg of the U-tube (see sketch above). The pressure will be expressed as In H2O, CM H2O, etc. Accuracy: The accuracy of the pressure generated by a simple U-tube manometer depends on the accuracy of the ruler or tape measure used to determine the height of the fluid column. If the tape measure used over 100 CM, for example, is marked in mm, then the fluid level can be determined to within one part in a thousand (0.1% FS). This is better than twice the accuracy of the 0.25% pressure transducer. Enhancement: For smaller fluid pressures, try slanting the U-tube. You will have to figure the trigonometry, but the fluid distance along the slanting tube will be the hypotenuse of a triangle whose opposite leg is the actual fluid head. So the fluid must travel further along the tube to raise the pressure. This increases the accuracy of the fluid pressure determination.