In order for a digital meter to be suitable for the educational environment, it must be precise enough to provide conclusive measurements. This means that the precision of the measuring device must be greater than that of the circuit components from which the measurements are to be taken.
Considering that the precision of resistors, bulbs, and other components used in schools varies from 5 to 10%, a meter should provide a minimum precision of 0.5% (at least 10 times bigger).
WHY NOT USE AN ANALOG METER?
When compared to digital meters, analog meters have the following disadvantages:
less precise (5%) and have a lower resolution
more difficult to read since the measured value is not indicated in numbers
more difficult to distinguish between bordering values
not as shock resistant due to the use of very fragile mechanical components (needle, mobile coil, etc.)
do not last as long as digital meters
have influence on the measured voltage.
It quickly becomes apparent that when it comes to teaching, analog meters do not provide measurements precise enough to be conclusive and are limited by their mechanical built. On the other hand, off-the-shelve meters are too precise and are not sturdy enough for the classroom/lab environment.
WHY NOT USE A MULTIMETER?
A multimeter is a very practical measuring device for an experienced user. However, because of the complexity of the device, it requires a great deal of attention from the operator. If the device is connected in parallel to a component (i.e. to measure a voltage) and the operator forgets to change the function selector (which was set for measuring the intensity of a current), the chances of damaging the multimeter are significant.
THE SIGMATRON SOLUTION
To meet these challenges, Sigmatron has developed a series of single-function digital meters: a voltmeter (V-24), two ammeters (A-20 and A-25), and an ohmmeter (O-20). These meters are precise enough for students to arrive at the proper conclusions and sturdy enough to survive most mishaps.
Furthermore, when comparing the average life expectancy of a $20 analog meter (a few months in the hands of students) with our 2-year guarantee, it is clear that Sigmatron meters provide a much better return on investment.
To help eliminate connection errors, there is a diagram showing how to connect the meter in the circuit as well as several indications on the overlay labels. These indications include practical hints that help students understand what they are doing during the experiment.
To further prevent confusion, these meters are the same color as their corresponding Mystery Boxes (A, B, C3 and C4 Series, sold separately), the ammeter is blue, the voltmeter is yellow and the ohmmeter is beige.
Models A-20, A-25 and O-20 feature a battery saving circuit that shuts off the unit after 90 minutes of use. This will ensure that the unit is properly shut off even if the user forgets to turn it off.
KEY FEATURES
This series of single-function digital meters has been especially designed to withstand extreme student abuse. To reduce risks of connection errors, the overlay labels feature a series of indications including practical hints to help students understand what they are doing during the experiment as well as a diagram showing how to connect the meter in the circuit.
In addition to providing up to 200 hours of usage on one 9-volt battery, Models A-20, A-25, and O-20 are equipped with a battery saver circuit that activates after a 90 minute delay.
These 3 1/2 digit meters offer an accuracy of less than 0.5%, an automatic reverse polarity indication (a minus sign (-) appears on the display), and a low-battery indicator.
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| Ref. | 20-03623 |
| Scales | 20 VDC |
| Resolution | 10 mV |
| Accuracy | 0.5 % |
| Maximum Reading | 1999 |
| Protection | Electronic |
| Color (overlay label) | Yellow |
| Power | 9V Battery (NEDA 1604) included |
| Battery Life | 200 hours of continuous use |
| Automatic Polarity | A minus sign appears on the display to indicate that the polarity is reversed |
| Battery Indicator | Appears on the display to indicate the battery needs to be replaced |
| Color (casing) | Yellow |
| Dimensions (L x W x H) | 88 x 170 x 38 mm |
| Weight | 315 g |
| Guarantee | 2 years, parts and labor |
