Parallax error occurs when analog instruments are viewed at an angle, causing inaccurate readings. Dwyer offers anti-parallax solutions, officially distributed in Vietnam by DLK.

Parallax Error

Understanding What It Is and How to Avoid It

When it comes to your application, as any process engineer can tell you, accuracy is everything. However, even the best-designed instruments can give misleading results if they are not read correctly. One of the most common causes of this is parallax error—a visual distortion that occurs when you view an analog gauge or dial from an angle instead of straight on (think of looking at a car’s fuel gauge from the passenger seat).

This small (and seemingly harmless) mistake can lead to significant consequences, from misjudging pressure levels in an HVAC system to misreading flow measurements on a production line. Understanding what parallax error is, why it occurs, and how to avoid it will greatly improve measurement accuracy and reliability for your application.

What is Parallax Error?

Parallax error occurs when a measurement is taken from an angle rather than from directly in front, causing the pointer (needle) of a dial instrument to appear at a different position relative to the scale.

In metrology, parallax error is considered an observational error—not a fault of the instrument itself. The device may be properly calibrated, but improper viewing introduces inaccuracy.

When Might You Encounter Parallax Error?

Instruments Prone to Parallax Error:

• Pressure Gauges
  Used in HVAC, process control, hydraulics

• Dial Thermometers
  Common in boilers, ovens, and refrigeration systems

• Flow Meters
  Analog displays are sensitive to viewing angle

Example: A technician checks boiler pressure on a dial gauge. From the side, it appears to read 95 psi. But from directly in front, the correct reading is 100 psi. That 5% error could lead to unnecessary adjustments, inefficiencies, or even unsafe conditions if not addressed.

Industries Where Parallax Error Matters:

• HVAC Systems: Misreading gauges may result in improper refrigerant charging or airflow adjustments

• Process Control: In food or chemical processing, even slight pressure or temperature deviations can impact product quality

• Power Generation & Labs: Engineering students often learn proper measurement techniques by observing how parallax error affects readings

How to Avoid Parallax Error

1. Read Gauges Straight-On

Ensure your line of sight is perpendicular to the pointer and scale. This eliminates angular distortion and gives a true reading.

2. Use Gauges Designed to Reduce Parallax

Some high-quality analog instruments feature a mirrored band or overlay behind the pointer. When the pointer and its reflection align, you know you’re viewing the gauge correctly.

3. Proper Installation

Mount gauges at eye level so technicians can easily take straight-on readings without having to crouch or lean.

4. Train Personnel

Operators and technicians should understand the cause of parallax error and be trained in proper observation techniques to ensure reliable readings.

Innovative Solutions from DwyerOmega

Series 2000 Magnehelic® Differential Pressure Gage

One of the most trusted gauges in the industry for HVAC, cleanroom, and process control applications.

• Clear, easy-to-read display: Undistorted plastic face and full-scale dial minimize misreading

• Durable construction: Die-cast aluminum housing with IP67 seal resists dust and moisture

• Precision mechanics: Patented diaphragm and magnetic movement provide stable readings

• Flexible installation: Flush-mount bezel for versatile panel mounting

• No power required: Mechanical operation = maintenance-free reliability

High Accuracy Magnehelic® Gage

For critical applications such as pharmaceutical or packaging environments.

• Twice the accuracy of the standard model (±1% over most ranges)

• Mirrored scale overlay eliminates parallax error

• 6-point calibration certificate included for measurement confidence

• Optional brushed stainless steel bezel offers corrosion resistance and a sleek design

Series RRT3 Remote Reading Thermometer with Switch

Dual-function device: Display + Control

• 3-1/4" dual-scale dial with process and setpoint pointers

• SPDT relay switch for control functions

• Front adjustment knob for easy setpoint changes

• 10.5 ft stainless steel armored capillary resists kinks and leaks

• Quick-connect terminals or finger-safe screws for easy installation

• Includes u-clamp for secure panel mounting

Applications:

• High-temperature process shutdown

• Boiler and chiller control

Contact the Official Distributor in Vietnam

For product consultation, technical support, or quotations on genuine Dwyer measurement instruments, please contact:

DLK TRADING SERVICE COMPANY LIMITED

📍 Representative Office: 111/7 Vuon Lai Street, Phu Tho Hoa Ward, Tan Phu District, Ho Chi Minh City

📞 Hotline: 070 357 0101
📧 Email: info@dlk.com.vn

DLK is committed to providing accurate, reliable, and technically compliant measurement solutions, along with dedicated support from our team of experienced engineers.

Contact us today for expert advice and a prompt quotation!