Scientific Analytical Calorimeter Solutions
 

How To Adjust the Sample Mass for Different CV

Introduction

The CAL3K needs to operate at the calibration conditions. Since it is measuring the temperature rise during the burning process the temperature rise of the sample is important.

The temperature rise is proportional to:

  • The mass of the sample
  • The energy in the sample (to be measured)

The calibration rise of 0.5g Benzoic Acid is approximately 12 Degrees °C. So, the sample rise should be approximately the same. The rise limits defaults are:

104 LOW RISE LIMIT 8 Degrees °C
105 HIGH RISE LIMIT 16 Degrees °C

These limits are 50% down and 33% up from the calibration rise of 12 degree °C. The limits are un-equal spaced because the heat losses increase more when going up. The Rise limits are parameters and can be changed from the keyboard.

Practical

The sample mass should be adjusted so that it produces a temperature rise which is approx. the same as the calibration rise. If the rise limits are violated then the CAL3K issues a warning. The warning can be ignored. Violating the high-rise limit should be avoided because it requires longer cooling time.

Here are the sample masses for calibration with 0.5g Benzoic Acid and the limits:

Expected CV (Kj/g) Expected CV(Kcal/g) Low Mass(8°C) Std Mass(12°C) High Mass(16°C)
35 8.4 0.29 0.38 0.58
30 7.2 0.29 0.44 0.6
26.5 (BA) 6.4 0.33 0.5 0.67
25 6 0.35 0.53 0.7
20 4.8 0.44 0.66 0.88
15 3.6 0.58 0.88 1.16

Conclusion

This is not science. If the CAL3K issues a Rise limit warning then adjust the mass accordingly. The adjustment is done to operate at the best accuracy. In most application the expected CV is known before a determination.

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