What affects the accuracy of a weight measurement?
Charder's scales are calibrated and certified according to medical standards prior to shipment. However, all scales can be affected by external factors that may have an influence on accuracy! Today, we'll introduce various factors that can affect accuracy, and give you some pointers on how to avoid them, so practitioners can receive the most consistent results.
1. The quality of the scale itself
If you have a lower quality scale, it can be difficult to receive the same level of accuracy and consistency, compared to one that's built and certified to medical standards.
At the core of every digital scale is a "load cell". When an object is placed upon the measurement platform, the load cell will physically bend (largely imperceptible to our eyes), and the degree to which the load cell is subjected to force is used to measure weight. What's the difference between low-quality and high-quality load cells?
Putting aside cheap load cells that are unable to measure weight accurately, even among load cells that can provide precise signals, there's always a balance between speed, consistency, and accuracy.
After force is applied to a load cell, it takes time to stabilize and send an accurate reading. Different industries will require different speeds ! For example, for fast-moving environments like mass manufacturing and checkweighing, a lightning-fast response time is critical. Manufacturers like Charder must excel at selecting the perfect specifications for any given model, providing customers with a good balance of affordability, speed, reliability, and accuracy.
2. The environment in which the scale is used
Temperature Changes: As we've learned in school, most objects expand with heat and contract with cold - load cells are no exception. Sudden, large changes in temperature can cause load cells to expand or contract, which can have an effect on measurement accuracy. This is why it's best to store scales indoors when possible, minimizing direct exposure to sunlight or cold environments.
Gravity: Gravity is often assumed to be the same everywhere on Earth, but it actually varies depending on location, because the Earth isn't a perfect sphere, and it's not uniformly dense! This is why medical scales need to be calibrated for location to minimize any error caused by a difference in geographical location.
3. Whether or not weight is loaded correctly
The way weight is loaded can also cause inaccuracies in measurement. First of all, a scale should be placed on a flat, solid surface that can fully support not just the weight of the scale itself plus the weight placed on the scale without any flexing or warping.
It also goes without saying that only the person being measured should be on the scale!
If other objects (such as a chair) need to be used because the subject cannot stand unassisted, you can first tare (subtract) the weight of the chair first before conducting measurement.
In addition, the entire weight of an object should be placed on the scale, or else the reading will be too light. So for example, if a patient is using a Chair Scale, their feet need to be resting upon the footrests:
If the subject's feet are on the floor, this will result in an inaccurate weight measurement!
4. External Factors
In addition to load cells, external interference can also affect the accuracy of a measurement, including:
Creep: If a weight is left on a scale for an extended period of time, the load cell is constantly under pressure, and the measured weight of the metal can change. Over a couple of minutes, this isn't a problem, but this is partly why it's important not to stack objects on top of your scale long-term, since it can warp a load cell and affect accuracy.
Vibration: Vibration from nearby machinery or powerful air conditioning units can be misinterpreted by load cells as weight. Ideally, a scale should be placed in a location free from interference.
Wind: This isn't really a factor for medical scales intended for measuring people, but for precision laboratory scales measuring in extremely tiny increments, even something like wind can affect results!
Air Pressure: Differences in air pressure can cause inaccuracy in measurement. For example, air pressure at sea level is a lot higher than at high altitude, so if the scale was originally manufactured in a factory closer to sea level, and you're using the scale in a high altitude location (ex: mountains), recalibration may be needed to optimize the scale for your location and ensure accurate results.
Moisture: Like all electronic products, digital scales can be negatively affected by condensation or moisture, which can cause the signals sent from the load cells to the display to be distorted and thus cause inaccurate measurement. If you're using a scale in a wet environment - such as a kitchen that's being hosed down - you want to choose one that has a high waterproof rating.
Electrical interference: Medical scales must pass Electro-magnetic certification to ensure that they won't be interfere with other electronic devices in their vicinity (and are resistant to interference as well), but non-medical scales may be more susceptible to being affected by such interference, with can influence measurement results.
Medically certified scales certainly are more expensive than your typical bathroom scale, but for good reason! Contact us to learn more about selecting the right scale for your facility.