Thursday, February 27, 2014

Mechanical Pressure Gauges Installation and Operating Instructions

Author: WIKA
From: WIKA Learning Center

Pressure Range Selection

To insure proper operation and long service life, the proper pressure range should be selected. For applications with constant, steady pressure, the measured pressure should be no more than 75% of the full scale range of the gauge. For applications with fluctuating pressure, the measured pressure should be no more than two-thirds of the full scale range of the gauge.

In general, it is best to choose a range that is roughly 2X the average measured pressure. This gives good over pressure protection and the highest accuracy.

Pressure Gauge Installation

The pressure gauge should be installed where exposure to heat and vibration are minimal and where the dial can be easily read. It is also important to install the gauge in a location with undisturbed and continuous flow of the pressure medium.

It is recommended that an isolating device, such as a needle valve or gauge cock, be installed between the process and the pressure gauges. This allows the gauge to be taken out of service without interruption of the process.

Connections with tapered threads, such as NPT, should be sealed by using PTFE tape (or an equivalent sealing compound) on the thread. Metric threads such as G1/4A or 1/4BSP should be sealed by using the appropriate sealing washer.

The gauge should be tightened and loosened using the wrench flats on the gauge socket. Never grasp the case to thread the gauge into the pressure system fitting. Doing so may cause irreparable damage to the gauge. For pressure gauges with flanged connections, care must be taken not to accidentally loosen the bolts that hold the upper and lower housings together.

A pressure gauge should never be removed when it is pressurized. Make sure the pressure system has been fully vented prior to removing a gauge.

Residues from the pressure medium may remain inside the pressure gauge after it has been removed from service. If these residues are hazardous or toxic, take the necessary precautions when handling and storing used gauges.


Isolating Devices

The isolating device may be either a pressure gauge cock or a needle valve, depending on operating conditions and requirements.

Pressure Gauge Cocks

Pressure gauge cocks have three handle positions:
OFF      The pressure medium is blocked and the
pressure gauge system is open to the atmosphere.
ON        The
pressure gauge is open to the pressure medium.
VENT   The
pressure gauge is isolated but the pressure system is vented and the medium can escape into the atmosphere.Pressure gauge cocks should be installed so that when vented, the pressure medium is directed away from the operator.

Pressure Gauge Needle Valves

Needle valves also isolate the pressure gauge from the pressure medium, but they usually do not have any venting capabilities. Needle valves do have the advantage of restricting the flow of the pressure into the gauge which helps reduce damage by pressure spikes.

Pressure Gauge Mounting Options

If the pressure system or tee-extension cannot support the weight of the instrument, then surface or wall mounting brackets or mounting flanges (front flange or rear flange) should be used.

Vibration Protection for Pressure Gauges

If the pressure gauge is exposed to vibration or pulsating pressure or both, then a liquid filled pressure gauge is recommended. The liquid dampens the effects of vibration making the pointer easier to read.


Pressure Gauge Temperature Limits

The pressure gauge should not be used outside of its rated temperature limits as noted on the Data Sheet specific to that gauge. At temperatures above or below these limits, the gauge accuracy will be significantly reduced and the possibility of gauge failure may exist.

Overpressure Limits on a Pressure Gauge

WIKA gauges are generally designed to withstand up to a 130% overpressure without damage to the pressure system. For applications with overpressure spikes, a snubber or restrictor should be used. Snubbers and restrictors reduce the inlet size of the pressure gauge which causes the pressure to increase or decrease more slowly into the gauge. For applications with periods of constant overpressure, an overpressure protector should be used. The overpressure protector isolates the gauge when the pressure reaches a preset pressure value.

Tee Extensions Guidelines for Pressure Gauges

Tee extensions should have a diameter of at least 0.24 in. (6mm) to avoid clogging from solids in the pressure medium. WIKA recommends that long, horizontal tee extensions be sloped to about 1:15.

With a gaseous pressure medium, the extension should having a drain plug at its lowest point, while a line with a liquid medium should have an air bleeding valve at its highest point. A filter or separator should be used when the pressure medium contains suspended matter.

If a static head of liquid is acting on the gauge, then this causes a zero offset which affects the reading of the gauge.

The corresponding indication will be lower by the value of Δp if the gauge is mounted above, but higher by the value of Δp if the gauge is mounted below the pressure tapping point.

Pressure Gauges in Service

Always open isolating devices slowly. Opening them too fast may generate sudden pressure surges that could damage the gauge.

Calibration can be confirmed in larger diameter gauges (> 4") by checking the position of the zero point. To do so, close the isolating device and vent the gauge to zero pressure. The pointer must over the zero box . Unless the gauge temperature is significantly higher or lower than 68°F (20°C), a pointer not returning to zero may indicate that the gauge has been seriously damaged.

Pressure Gauge Storage

The pressure gauge should remain in its original packing until installation.

Storage temperature should not exceed -4°F (-20°C) or 140°F (60°C) unless specified otherwise. Consult the data sheet pertaining to the pressure gauge model.

Pressure gauges removed from service should be protected from dust and humidity, preferably by using the original packing material. Residue from the pressure medium may remain in the gauge and is susceptible to temperature influences (i.e. freezing). This should be considered when storing the removed pressure gauge.

Pressure Gauge Safety

Pressure media such as:
  • Oxygen
  • Acetylene
  • Flammable gases or liquids
  • Toxic gases or liquids
  • Steam
  • Ammonia and other refrigerants
as well as portable or stationary pressure systems like:
  • Air compressors
  • Welding equipment
  • Pressure vessels and boilers
  • Life support equipment
may require pressure gauges that have been tested and/or certified to national standards and/or local safety codes. Your local WIKA representative will be able to assist you in selecting the proper gauge model.

Standards for Pressure Gauges

U.S. & Canadian Standards are set forth by The American Society of Mechanical Engineers, which publishes pressure gauge specifications in their document ASME B40.1. This document specifies standard pressure gauge types, sizes, materials, ranges, and accuracies. Copies of this standard can be purchased directly from ASME:
22 Law Drive, Box 2900
Fairfield, NJ 07007-2900
1-800-THE-ASME or (973) 882-1167
Fax: (973) 882-1717
European Standards are developed and published by the European Committee for Standardization (CEN) and replace the individual standards formerly used in each European country (such as DIN standards in Germany). Copies of these standards can be obtained through:
Comité Européen de Normalisation (CEN)
Central Secretariat
rue de Stassart 36
B-1050 Brussels

Pressure Gauge Accessories

  1. Over Pressure Protector
  2. Throttling (adjustable) Snubber
  3. Adaptor for wall mounting bracket
  4. Needle Valves
  5. Coil Siphon
  6. Wall Mounting Bracket
  7. Thread Adaptor (1/4" NPT - G1/4A)


Recommended Pressure Gauge Orientation

The table below shows the recommended position for pressure gauges in typical applications.
If you would like to receive more information about WIKA pressure gauges please contact Forberg Scientific, Inc. customer service.
Phone: 855-288-5330

Wednesday, February 26, 2014

Hall Effect Zero Speed and Active Sensors

Hall effect speed sensors are also called Zero Speed Sensors and Active Speed Sensors


Hall Effect Sensors:

  • Is an active, powered device that produces an output signal regardless of target speed from zero 15kHz+
  • It includes a silicon chip that has high level of circuit integration leading to high reliability
  • Typical output from a Hall Effect Sensors is Digital, square-wave output; amplitude is independent if speed
  • 3 wire connection (single channel), 5 wire connection (dual channel with direction)
  • Very stable over wide temperature range -40C to +125C

Principle of Operation - Single Element vs. Differential

Single Element
RH Series - no need for alignment
BH, DH Series - requires alignment

Hall Effect Speed Sensor Features:

  • High temperature range of -40C to +125C
  • Wide range of supply voltage; 4.5-24Vdc (single channel) and 10-28Vdc (dual channel)
  • Two output options of Supply Tracking or TTL Compatible
  • Increased air gap capability over VR Sensors; no loss of signal amplitude
  • Output signal will react to the lowest increment of speed without loss of amplitude
  • High level of intrinsic noise immunity
  • Vibration Immunity

Hall Effect Speed Sensor Benefits:

  • Easy installation
  • No alignment for RH series sensors
  • High reliability
  • Direction Indication
  • Reverse voltage protection, up to -30 Vdc, to prevent damage if mis-wired

Hall Effect Speed Sensor Limitations:

  • Temperature - Max temp is 125C
  • Not good with axial trajectory targets

If you would like more information about the Aitek Speed Sensors or other Aitek Products please contact Forberg Scientific, Inc.
Toll Free: 855-288-5330

Websites: &

Tuesday, February 25, 2014

How Variable Reluctance Speed Sensors Work

How AKA Passive Speed Sensors Work:


Variable Reluctance (Passive Speed Sensor)

  • Magnetic resistance is known as reluctance (variable reluctance = VR).
  • Each tooth positioned in front of the pole decreases reluctance and increases magnetic field density around the coil
  • Each valley increases reluctance and causes the magnetic field to collapse around the coil thereby generating a voltage.
  • Repeating combination of tooth & valley, such as found on a gear, create a sinusoidal electrical output signal.
  • As the rate of change of the magnetic field increases, so does the amplitude

Variable Speed Sensors Features:

  • Senses gears or any ferromagnetic discontinuity
  • No moving parts or contacts
  • Two Wires (No Power Req'd)
  • Harsh environments (pressure or chemical)
  • High ambient Temperatures - (750 F / 400 C max) 

Variable Speed Sensors Benefits:

  • Easy installation
  • No alignment
  • High reliability - mature technology
  • Low Cost

Variable Speed Sensors Limitations:

  • Poor low speed performance (below 100RPM / 15 IPS)
  • Output amplitude dependent on speed and air gap
If you would like more information about the Aitek Speed Sensors or other Aitek Products please contact Forberg Scientific, Inc.
Toll Free: 855-288-5330

Websites: &