Digital Weigh Scale types

Weighing scales can be broadly classified into-

1. fixed
2. portable

Fixed scales can be classified as below-

Fixed Type	Description	Weight Range
Dormant scale	This scale is fixed in a pit such that it's top surface is in level with the floor. Heavy objects like cylinders/barrels can be rolled on to the scale for easy weighing. Dormant scales are commonly used in gas-filling areas to monitor cylinder weight. Filling takes place with the cylinder placed on the scale. On reaching the limit filling is cut-off or an alarm is sounded to alert the operator.	100kg to 10000kg
Tank/Hopper/Silo weighing system	Weighing system is built into the structure of the tank support. Load cells are positioned to take the tank/hopper/silo's weights. This system helps monitor/control material stock/movement.	500kg to 20000kg
Conveyor weighing system	A conveyor weighing system measures rate of flow of material- tonnes per hour (TPH). It is commonly used in industries such as mining, cement, fertilizer, etc. Load cells are fixed into under the conveyor belt which senses the weight at that point. The system includes other components like proximity switch to monitor speed. A special digitizer calculates TPH using input from load cells and proximity switch. Conveyor weighing system helps monitor/control rate of flow of material which is a critical parameter in process industries.
Crane weighing system	A weighing system is built into the structure of the crane. Load cells are positioned to measure the load lifted by the crane. This system helps avoid overloading. It is also used to monitor/control material stock/movement.	500kg to 20000kg
Filling/Packing system	A Packing/Filling system is commonly used in industries liquid or solid material are packed in containers like plastic bags, cardboard cartons, cans, bottles, etc. The system measures and fills the container with the specified quantity. Load cells installed in the system are connected to a special purpose digitizer cum controller which monitors & controls material feeders. Packing/Filling systems are common in food, sugar, cement, fertilizer, etc.	200g to 50kg
Check weighing system	A check weighing system is commonly used in industries where material (liquid or solid) is packed in containers like plastic bags, cardboard cartons, cans, bottles, etc. Check weighers are used to ensure that material quantity is right- not less or not more. The system alerts the operator whenever a package falls outside the specified limits. Some systems automatically send non-qualifying packages to reject bin. Check weighers are normally built into the conveyor system on which packed material move. Load cells installed in the system are connected to a special purpose digitizer which monitors weight data of every package moving over the conveyor.	50g to 200kg
Weigh bridge	Also called truck scales, these scales are used to weigh commercial vehicles like trucks and trailers. Weigh bridges are a must for medium and large manufacturing industries.	20T to 100T
On-board truck scale	Load cells are mounted on the truck chassis and connected to digitizer in the driver's console. This system measures the weight of the material in the truck/tipper. Onboard weighing is used as a safety feature or to track material movement continuously.	10T to 200T
Rail weighing system	Rails are modified to accommodate strain gauges and hence work as load cells. Such rails, installed in the tracks and connected to a digitizer, help measure railcar weight. The train need not stop for the measurement- weighing is done in-motion.	100T to 500T
Off-Road Truck Scales	These scales are heavier versions on truck scales. Heavy tippers used coal/iron ore mines use such scales to track material movement.	50T to 500T
Weigh-in-motion system	These systems are used to check overloading of commercial vehicles on highways. A weigh bridge positioned under the surface of the road measures the weight of truck/trailers while the vehicles are in motion.	100T

Portable scales can be classified as below-

Portable Type	Description	Weight Range
Laboratory scale	Laboratory scales are made for high accuracy-high precision measurement of light objects weighing few grams. These scales are delicate & sensitive and need to be handled with extreme care. Most cases these scales are placed in a special enclosure to protect the scale from dust, moisture and even blowing air. Test weights or objects to be weighed are handled with forceps, not with bare fingers.	10g to 1kg
Human scales	Human scales designed for home/clincal use are generally low accuracy scales. Compact floor models are the most commonly ones used to weigh human beings other than infants. There are other special types for the disabled- wheel chair scales or scale mounted stretchers. To weigh infants and small kids, baby scales are employed by hospitals.	200kg
Table top scale	Table top scales are used for weighing light weight objects. Retail stores is the biggest market for these scales. Dealers offer various models- low-cost to high precision/high accuracy models. These scales are easy to use and easy to maintain but delicate and need to be handled with care.	10kg to 30kg
Bench scale	Bench scales are low capacity scales mainly used at a retail stores. Most scales are simple low-cost, easy to use, easy to maintain devices which can be purchased of the shelf.	30kg to 50kg
Platform scale	Platform scales are available in low to high capacities having a wide range of applications right from a retail store to a warehouse to a manufacturing setup. While lower capacity scales have one load cells, higher capacity scales come with four load cells. Scale manufacturers/dealers offer simple low-cost models to expensive custom-built models with extended features like connectivity to PC or ticket-printing facility.	100kg to 500kg
Floor scale	Floor scales are designed for heavy-duty usage in industrial, manufacturing or warehouse setting. These scales usually have a two steel frames- lower and upper- between which four load cells positioned. Objects to be weighed are placed on the top deck plate which is fastened to the top frame. Load cells are connected to a digitizer via a junction box. Digitizer can be a simple weight indicator or possess advance features to transfer weight data to a PC where data is captured & stored for further use like generating reports on material movement.	200kg to 1000kg
Pallet weighing scale	Pallet Weighing Systems (PWS) helps weigh load on the spot or as it is being handled. PWS are commonly used in manufacturing setups to track material movement. Load cells and necessary accessories are integrated into the pallet truck frame so that load cells sense the weight of the material handled. A battery powered digitizer powers the load cells and displays weight on a ergonomically positioned display.	500kg to 2000kg
Hook Scale	Hook scales is a compact device with a tensile load cell and digitizer components housed in special enclosure. The load cell has hooks fixed on both ends- upper hook for hanging the scale and lower for hanging the object to be weighed. Hook scales are commonly used in cranes in loading area so that weight of the material can be checked. They are also used in production area to ascertain weights of various objects. They can also be used as safety equipment in cranes while hoisting delicate or sensitive items.	500kg to 2000kg
Livestock scale	Livestock scales or cattle scales are commonly used on farms to weigh animals. These scales are designed to accommodate the animals and coated with special paints or coatings to resist corrosive properties of animals wastes. Livestock scales are easy to carry, setup and use.	100kg to 500kg
Ramp-End Scale	Weigh pads or Portable Ramp-end Scales help weighing vehicles on any level surface. Weigh pads are used to check weight distribution on wheels/axles. These light weight and low profile scales can be carried around in a car or a van. Setting up the scales is simple- just position scales to match axle width & wheel base and connect to digitizer. The battery powered digitizer powers the weigh pads and displays weight- individual wheel weight, weight on each axle or total weight. Portable Ramp-end Scales are useful to vehicle manufacturers, car racing teams, fleet owners and highway authorities (to check overloading of vehicles).	5T to 10T
Aircraft weighing system	Aircraft weighing systems are similar to Portable Ramp-end Scales. AWS is used to check weight distribution on the wheels and also to measure total weight of the aircraft. These light weight and low profile scales can be carried around and set-up easily. Normally the aircraft to be weighed is jacked up, weigh pads positioned under the aircraft and then lowered down so that it rests on the weigh pads. A battery powered digitizer powers the weigh pads and displays weight- weight on each of the pads and also the total weight. AWS are useful to aircraft manufacturers and aircraft maintenance companies.	2T to 10T

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How does a Digital Weigh Scale work?

Imagine you pick an apple and try to guess it's weight. You would place it in your palm and toss it lightly to feel the weight. After 3 or 4 tosses you would say "200 grams". Your hand sensed the weight and sent a signal to your brain which after some calculations estimated the weight. Right? Similarly, when you place the same apple on a digital weigh scale, the load cell senses the weight and sends the signal to the indicator. The signal conditioner processes the load cell signal and displays weight.

Basically all weigh scales consist of-

• a structure
• one or more load cells
• signal conditioner

Structure is the load bearing part. It transfers the weight to the load cell(s). In low capacity scales (table-top/bench/platform) the structure houses the load cell and electronic components. In higher capacity scales (floor/dormant/weigh bridge) the structure rests on load cells. The weight indicator

Load Cell is basically a transducer which converts force into electrical signal. Every digital weigh scale has one or more load cells. Table-top/Bench/Platform scales are single load cell weighing machines. Floor/Dormant scales have four load cells. Truck scales or Weigh bridges have 4 to 8 load cells depending on the rated capacity and length of the bridge. For all scales load cell is the part which determines the scales rated capacity. Of course the mechanical structure is designed to withstand loads well beyond the rated capacity. Load cells capacities range from 500g to 100T.

Signal Conditioner is the electronics part, it powers the load cell, receives signal from the load cell(s) and converts that signal to readable numbers. The numbers- digital output- can be made to display in desired unit of weight. Signal conditioners have extended features like RS232 or 4-20MA output which can be used for data acquisition or control other electrical equipment. An electronic weigh scale hooked up to a computer can automate many aspects of business operations like materials management or process control or billing automation.

Compare a mechanical scale to an electronic scale. Mechanical scale just shows the weight but an electronic scale does much more than that- it helps automate.

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Rated Capacity & Accuracy

Digital weigh scales come in various capacities- starting with jewelry scales (to weigh few grams) to weigh bridges (to weigh mining trucks weighing hundreds of tons). The maximum weight a scale can measure is called Rated Capacity.

Accuracy is an important characteristic of any measuring instrument. We have high, medium and low accuracy scales.

Low - kitchen scales and bathroom scales (non-commercial scales)
Medium - scales used for business purposes
High - scales used in labs or for scientific research

For commercial purposes accuracy is considered as 1/10000th of Rated Capacity. While jewelry scales measure grams with milligrams accuracy, weigh bridges weigh tons with kilograms accuracy. Example; accuracy of a 30T weigh bridge is ±5Kg. Accuracy defines the Least Count - the value with which the weight increments or decrements in the display.

Example 1; display value in a 10kg scale increments as shown below-
01.996 Kg
01.997 Kg
01.998 Kg
01.999 Kg
02.000 Kg

Example 2; value in a 30T weigh bridge increments as shown below-
20.080 T
20.085 T
20.090 T
20.095 T

Also there's another important parameter- Minimum Weight - the least possible weight that a scale can measure for the specified accuracy. It's not practical to measure 2kg on a 100kg scale or to weigh 200Kg on a 30T weigh bridge because we loose out on accuracy. It's ideal to use a 10Kg scale to weigh 2Kg and a 500Kg scale to weigh 200Kg. Minimum weight is normally considered 20 times Least Count.

Table below shows standard values of Least Count, Accuracy and Minimum Weight for some Rated Capacities.

Type of scale	Rated Capacity	Least Count	Accuracy	Minimum Weight
Laboratory	100g	0.01g	±0.01g	0.2g
Jewelry	500g	0.1g	±0.1g	2g
Table Top	10Kg	1g	±1g	20g
Bench	50Kg	5g	±5g	100g
Platform	100Kg	10g	±10g	200g
Floor	5000Kg	500g	±500g	10Kg
Weigh Bridge	30T	5Kg	±5Kg	100Kg
Weigh Bridge	100T	10Kg	±10Kg	200Kg

However scales with better accuracies are available. Naturally high accuracy scales would cost more than the standard ones.

'Dual Range' is another popular feature in jewelry, table-top, bench and platform scales. These scales measure lighter loads with high accuracy and switch over to lower accuracy for heavier loads.

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