Introduction

Balances are used for both sample weighing and dispensor calibration. The best balance to use depends on the accuracy required, frequency of use, approximate weights to be determined, as well as the type of material being weighed.

Balances available from UDY Corporation are chosen because they provide a practical combination of sensitivity, ease of use, ruggedness and accuracy at reasonable prices. An Electronic Balance provides high sensitivity and high capacity as well as speed and easy use. The preferred sensitivity of the Balance should be 0.001 grams. The Electronic Balance is the preferred method of sampling because of the accuracy instead of other methods such as syringe pipetting. As a general rule, all weighing should be to within 2 parts per 1000 (0.2%). Consult UDY Corporation for recommendations on Balances.

Sample Weighing

General Information

Since a great deal of time can be lost in sample weighing when specified weights must be measured out, a few tips are appropriate. As experience is gained, most people become good at estimating the approximate sample size and can weigh samples quickly.

Samples should be ground and mixed thoroughly so that the relatively small portions tested will be representative of the whole. When samples might change moisture content quickly, they must be handled rapidly to minimize the weight changes. The Balance should be positioned convenient for the analysis flow (sample preparation, weighing reagent dispensing, reaction then measurement). It should be away from drafts or the air currents and on a surface free from vibrations.

Weighing should be within 0.2 percent of sample weight to prevent weighing errors from affecting results.

Scoopula for Powdered Samples

The following points should be followed when using the SCOOPULA for powdered samples:

1. Use the blunt and not the tapered end to minimize spillage.

2. Scoop out slightly more than the specified amount of sample, if possible without spilling over the side of the SCOOPULA.

3. Hold the SCOOPULA between the thumb and fingers, keeping the index finger free. Tap the SCOOPULA with the index finger to transfer sample from the SCOOPULA.

Electronic Balance

Set-Up

Remove the balance from its shipping carton, and set it in the desired position for use. Install the weigh pan, and plug the power cord into a grounded receptacle providing the proper voltage. Turn the Balance ON, and allow it to warm up at least 20 minutes. Place range switch in desired position. Tare the reading to zero, then place a 20 to 30 g weight (Class p or S) on the pan and observe the reading. If the reading is not correct, the calibration needs adjustment. Refer to the Manufacturer's manual. Repeat calibration check and adjustment until the proper reading is obtained. NOTE: Calibration adjustment is usually required with relocation of the Balance because of altitude changes and other

influences on Balance. Additional information is given in the manufacturer's instructions

included with the Balance. If calibration weights are not available, contact UDY personnel for assistance.

Use

Place range switch in appropriate position, then place sample container on Balance pan. Tare out sample container weight, then add specified sample amount. Use caution to avoid spilling samples around the Balance pan support.

Maintenance

Clean up spills immediately. Dust or other particles entering the balance through the pan support opening will cause erratic readings.

Recheck calibration whenever balance operation is questioned. If balance readings are unstable, likely causes are: 1) air drafts; 2)static electric charges; 3)unstable line voltage or excessive power line "noise". If unstable readings are caused by air drafts, eliminate the draft or add a shield. In some cases, an inverted plastic bowl with an opening cut in the bottom can be left in place without interfering with the balance use and yet provide sufficient draft protection. Static charges can be eliminated by grounding one's body and the objects being weighed. Consult UDY Corporation or balance manufacturer if operational difficulties arise that cannot be resolved after reviewing the manual prepared by the manufacturer and included with the balance.