Bench Scales

Bench scales are available in many platform sizes and configurations. The platform sizes range from about 6" x 6" to 24" x 24". Smaller scales are generally referred to as electronic balances. They may have brackets or a column to make the scale and digital indicator one piece or some way to wall mount the digital indicator. It is normally best to have a one piece scale if you are planning to move the scale to different locations and conversely if the scale is to remain in one location the digital indicator can be wall mounted. Bench scales with the display below the platform are available and are usually configured this way for retail price computing, counting and simple weighing applications. Within the bench scale catagory are simple weighing scales, checkweighers, shipping and receiving scales, stainless steel bench scales, counting scales and all purpose scales which can be used on a bench or on the floor. Bench scales can be powered by 120/230 VAC, batteries, internal rechargeable batteries or with an internal or external charger. Most scale platforms have a stainless steel cover. The frame can be either mild steel, stainless steel or cast. All stainless steel scales are best for wet, chemical, or washdown environments. They will last many years and are easy to repair if this should become necessary. Scales with mild steel frames are fine for most dry environments. The weighing range of bench scales is from about 2 lbs. to 1,000 lbs. and they have a displayed resolution from 3,000 to 10,000 divisions with 5,000 divisions being the most common.

Floor Scales

Floor scales can be installed on the floor with or without a ramp or ramps, or in a concrete pit for a flush with the floor installation. Pre- fabricated pit frames are available or they can be made on site. The pre- fabricated frames are made in the manufacturer's jig and more reliably accurate as well as inexpensive when all the fabrication costs are totaled. Floor scales are available in sizes from 2.5' x 2.5' to 8' x 10' and capacities from 500 lb. to 30,000 lbs. The standard number of graduations displayed by floor scale is 5,000. For example a 5,000 lb. scale would have a 1 lb. division and a 10,000 lb. scale would have a 2 lb. division. As with all scales it is better to use a higher capacity than necessary (to a degree) for the application if the scale graduation (the higher the scale capacity the larger the graduation) is acceptable for the process and accuracy requirements. The environmental concerns for a floor scale are water, dust, and chemicals. If your environment is washdown as in a food plant the best type of scale to use is a stainless steel platform with hermetically sealed load cells and a NEMA-4X junction box. In a dry environment a mild steel platform and environmentally sealed load cells are sufficient. Stainless steel is the best for chemicals. A dust tight enclosure for the scale's digital indicator is best for most applications and a NEMA-IVX enclosure is necessary in washdown environments. In severe washdown environments a digital indicator can be installed in a separate window enclosure with remote switching for the front panel functions needed. A remote enclosure can be used for a floor scale load cell junction box if water intrusion becomes a problem. Ramps can be used for pallet jack access to the scale but are not needed or recommended for forklifts. A forklift can overload the load cells if driven up a ramp and onto the scale while carrying a load. If forklifts are damaging your scale you can try anchoring angle iron to the floor in front of the scale to stop forklift tires. Keep the top of the angle iron below scale deck height.

Weigh Modules and Load Cells

Load cells are available in a multitude of sizes shapes and configurations. Weigh modules containing a load cell and load cell mount are designed for mounting of tanks, hoppers, conveyors, weighbridges and just about anything that you would like to become a weighing device. Load cells are constructed of steel alloys, aluminum or stainless steel. The two types of sealing used in load cells are environmentally sealed and hermetically sealed. The load cell gauge area in an environmentally sealed load cell is filled with a flexible potting agent. A hermetically sealed load cell's gauge area is purged with nitrogen and a welded cap forms the seal. Some also have a glass to metal seal at the cable entry. The configurations are S-Beams, Single-Ended Beams, Double-Ended Beams, Compression Cannister, Single Points, and small sensors such as tension links, button type sensors, and washer force sensors. S-Beams are used for hanging vessels and usually incorporated in an isolated tension cell mount (ITCM) which reduces errors from side and twisting forces, electrically isolates the load cell from stray currents which can damage load cells, and provides additional safety. Single-Ended Beams, Double-Ended Beams and Compression Cannister are generally used in the Weigh Modules described above. Single points are generally used in bench scale platforms containing a single load cell in the center under the platform frame.

Electronic Balances

Electronic balances use technology enabling them to accurately display from approximately 20,000 to over 4 million divisions. The cost of an electronic balance is generally directly proportional to the amount of graduations that it can display. This technology is a delicate combination of mechanical and electronic construction making an electronic balance more susceptible to damage from overload and expensive to repair. It is for these reasons that electronic balance use is not recommended in a production environment. A lab environment has the characteristics more viable for the electronic balance. A solid, flat, vibration free bench or table, constant temperature and less air currents are what an electronic balance needs for accurate weighing. Top loading electronic balances with up to a .01g graduation can normally be used without a breeze break but when the graduation becomes .001g or less a breeze break is needed. With a graduation of .001g and less manufacturers will include a breeze break one with the balance and a better one with sliding glass doors on both sides and top is optional. Balances be calibrated at the site intended for their use as temperature and geographic location will effect accuracy. IMPORTANT! -- Balances must be leveled before calibration and kept level to maintain accuracy. Most manufacturers produce balances with adjustable feet but some do not. We advise the purchase of a balance with adjustable feet and a level vial as out of level conditions can cause considerable errors. When a balance is calibrated in a level condition the user has a reference that insures the repeatability of the calibrated accuracy. If a balance is moved after calibration it must be re-leveled to maintain accuracy. All benches are not exactly level which leaves the leveling feet with this job.

Some compact balances available are load cell based. They will display up to about 20,000 divisions and are considerably less expensive than electronic balances. If the intended use is a production environment a compact balance is a good choice.

IMPORTANT! -- Balances must be leveled before calibration and kept level to maintain accuracy. Most manufacturers produce balances with adjustable feet but some do not. We advise the purchase of a balance with adjustable feet and a level vial as out of level conditions can cause considerable errors. When a balance is calibrated in a level condition the user has a reference that insures the repeatability of the calibrated accuracy. If a balance is moved after calibration it must be re-leveled to maintain accuracy. All benches are not exactly level which leaves the leveling feet with this job.