EQUIPMENTS FOR WEIGHING/Analytical balance/Electronic balance/ Direct read-out top-loading balanc

EQUIPMENTS FOR WEIGHING:-Weighing equipments are essential in a medical laboratory. They are used to weigh substances for the preparation of reagents. Weighing balances, have different sensitivity ranges depending on the nature and amount of the substance to be weighed.

There are three types of balances which are very useful in the laboratory. They are:

1. Analytical balance

2. Electronic balance

3. Direct read-out and top-loading balance.

 1. Analytical balance- Analytical balance is basically a two-pan balance. It has a simple operation by which a set of known weights is added in one pan while the other pan is balanced by the substance being weighed. This type of balance is fast fading out.

A modification of the balance described above is the single pan balance. Attached to one end of the balance is a beam with a weighing scale on it. Before weighing a substance, the scale is set to zero with the aid of a knob at the other end of the beam. A substance is weighed by moving the scale on the beam to achieve equilibrium.

These balances take a maximum load of about 200 g with a sensitivity of 1 mg.

2. Electronic balance The advent of microprocessor in the field of electronics has brought about the introduction of extremely sensitive electronic balance. This type of balance corelates weight of a substance with electromagnetic force. It is a mono-pan balance, supported by an electric coil which is suspended in an electromagnetic field. Adding weight to the pan causes the coil to move. This movement changes the electric current within the electromagnetic field. This change is proportional to the weight of the substance, and is measured with an indicator system. The electronic balance, though expensive, offers accuracy, speed and ease of operation.

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3. Direct read-out top-loading balance There are two versions of this type of balance, electric or electronic. The electric one is less expensive and more robust. The two versions have the same advantages of being easy and quick to use because the weight of the substance is seen on the direct read-out scale. They also have a device which com pensales for the weight of the weight container

Prnsates for the weighr of the weighinh container case of a laboratory balance :- laboratory balances are delicate precision instruments which require careful handling and regular maintence.

The manufactures instructions for use area to be followed  as much as possible, the simple rules for the care and maintenance of the balances are:

1. Position the balance on a vibration-free even surface, preferably in a draught-free area.

2. Level the balance with the help of a spirit level by adjusting the screws on the stand.

3. Zero the balance before weighing.

4. Always use forceps to add or remove weights when using a pan balance.

5. Never weigh any substance directly on the pan of a balance, use a weighing container.

 6. Keep the balance and the pans free of chemicals by brushing the pans off after use.

7. Always keep a dessicant inside the cabinet of analytical balance.

8. Check the accuracy of the balance regularly.

9. When not in use, protect the balance with a cover