Selecting the Right Gauge and Pressure Range
Measuring pressure can be a challenging process at times. There are risks and safety precautions that should be addressed when dealing with high pressure and dangerous media consisting of gas or liquid. We designed the following features in the Vaetrix ETG Series to minimize risk should a mistake or error occur while performing a measurement or calibration.
Clear warning when the maximum full-scale pressure of the device has been reached
Display indicates OVER RANGE or UNDER RANGE with visual bar graph 0-100%
Ability to set high or low-pressure alarms with visual notification (icon and red display)
Ability to clearly view the min, max, and live pressure on the display at one time
Dedicated screen for min/max
True graphics display with selectable backlight color for different light conditions
Provide a safety factor for accidents
Burst pressure of 2x or greater for all pressure ranges
Easy to use and ability to customize the menu features that are important to the end user
Menu driven interface with words, no encrypted symbols or operation manual required
Turn on or off menu options under the admin function
Standard product stands up to abuse without the need to purchase additional options
Standard 4 Year Warranty
Product comes standard with NIST certificate with data, batteries, and protective rubber boot
Range: You will notice that we clearly tell you the full-scale range or span of the products. The accuracy is rated throughout the operating range of product. There are many choices when it comes to range accuracy, we make sure this includes linearity, hysteresis, and repeatability on all products. We don’t play specsmanship games or hide the compensated pressure range in fine print. If the product is rated for percent of full-scale, take the accuracy specification and multiply it by the value. This will be your ± accuracy value when using the product.
Example: -12 to 100 PSI @ ±0.05% Full Scale (Positive Pressure)
100 * 0.0005 = ±0.05 PSI
Selecting the proper pressure range of product is very important when you look at the overall big picture as well. Typically, you would like to strive to meet a 4:1 Test Uncertainty Ratio (TUR) whenever possible with a minimum of 2:1 (TUR). If you are using Test Accuracy Ratios (TAR’s) to keep things simple and dealing with uncertainty ratio independently, the values may change. We report the uncertainty of each measurement on the NIST certificate with data provided to you with each product.
Why are uncertainty or accuracy ratios important? If there is an Out of Tolerance condition on a calibration standard used in the field, it gives you some wiggle room for error to avoid recalls or an impact on a process. It is always a good idea to check with your quality assurance or designated person to ensure compliance with company policy when purchasing calibration standards. If you are still confused on ratios, the American Society for Quality (ASQ) may be able to help.
Media: At Vaetrix, we calibrate and exercise each sensor that is used for any of our products. The majority of these sensors have a welded stainless-steel diaphragm which isolates the media from the sensing element. There is a tiny amount of air-evacuated oil, generally silicon, which acts as dampening device. These sensors are designed to take abuse, and are great for end users that may not know exactly what is in the process or line they are calibrating.
In low pressure range applications, generally under 15 PSI, we will use non-isolated sensors. They are more sensitive to pressure changes and tend to respond better as the sensor substrate is directly exposed to the media. These sensors also perform better over time when a hard, full vacuum is applied to the sensor. The stainless-steel diaphragm typically does not like to flex in both directions, will notice the gauge will have a hard time maintaining a steady zero or tend to drift. The downside of using a non-isolated sensor is that they are not intended for liquid or moisture and will fail overtime. To make things clear, we tell you up front what each product/sensor is designed for by using the following terms in our part number configurator:
I = Isolated (Gas and liquids compatible with 316SS)
C = Compound (Clean dry, gas)
A = Isolated Absolute (Gas and liquids compatible with 316SS)
Calibration: We rate our products over a year for stability. It is recommended the product be calibrated on annual basis to meet published specifications. The interval can be extended overtime based in usage, calibration history, uncertainty ratios, contract specifications and several other factors. It is up to the end user and their quality assurance program to establish the calibration interval. Here is a great article from the National Institute of Standards and Technology that covers calibration intervals in detail.