App Note: AC Voltage Readout with CAL5000
If you have been using your CAL5000 for some time to verify the
readings of your various testers, but have not yet used it to verify AC
voltage, this note should be helpful for you. It is not uncommon to find
simple Go/No Go testers in workshop environments. A Crown 2109 is what would be called a High Potential Insulation Tester. It has several set points for output voltages, 500 V, 1000V, 2750V etc. It is important to verify that when you select a test voltage, you are actually getting it..
AC voltage, by it's very nature, is a voltage charging in amplitude, versus time. Because of this, capacitive and inductive effects can affect measurements. This app note helps put you on the right track.
The CAL5000 has a special voltage divider circuit, that has a very high impedance. The high impedance is about 1000 Meg Ohms. e.g. When 1000 volts is applied to the input, a proportional 1 volt signal is seen at the output.
The Crown 2109 was connected across the 1000:1 voltage divider circuit. In this case, the test leads from the Crown 2109 were temporarily attached to the inputs.
On the right side of the photo, you will note the copper clamp directly attached the the ground plug on the CAL5000. This copper clamp is the return from the Crown 2109 test leads.
The 1000:1 output circuit was fed directly into a multi-meter, as shown below.
The banana jacks from the 1000:1 divider are applied to a meter with 10 Meg Ohm input impedance. An example of such a multi meter is seen to the left.
A series of tests were performed with the CAL5000 and the Crown 2109, just as you saw it connected here. The results were not what was expected, with values that reported on the Fluke 77 that did not make sense. The values readout by the Fluke 77 were "crazy inconsistent" and calibration verification was not acceptable. Inconsistent Results:
Crown 2109 Output
Voltage Selector (VAC)
1000:1 Divider Output V
w/missing ground Ref (VAC)
|Crown Voltage suspected||Problem: Floating measure-|
|to be out of tolerance||ments! = inconsistent results|
The problem was solved by placing an earth ground on the CAL5000 ground plug. The readings were "floating". When a high impedance circuit is "floating" it tends to assume a random, stray voltage. This can result in inconsistent readings.
The ground was obtained at the protective earth on the engineers/technicians workbench. Here are the results:
|1000:1 Divider Output||% Error|
|Voltage w/ground reference (VAC)||Crown Versus CAL5000|
|Stable readings with Grounded Measurement Circuit|
Found OUT of TOLERANCE
Note: The CAL5000 multiple vendor adapter kit includes a jumper, for this purpose.
A Crown 2109 was found out of tolerance, and sent out for repairs. The CAL5000 proved it's value by confirming the apparatus was out of tolerance. CAL5000 can be deployed regularly to provide confidence in readings from many types of test equipment. This can be done periodically, versus waiting for 12 or more months between calibration certifications. This is the elegance of the Calibration Verification System.
App Note: Verification of Test Results
Background: The electrical test supervisor at the shipyard
overhaul shop was testing the winding resistance of a
shipboard transformer. The reason was that the transformer
had been pulled for inspection and overhaul. Of course, he
was on a tight timetable, BUT he was getting readings he was not comfortable with.
His winding resistance readings were 0.008, 0.009 and 0.009 ohms for the primary phases of the transformer. Having tested this particular type of transformer before, he was suspicious his resistance bridge was performing improperly. But, he could not condemn the resistance bridge, or the transformer without a verification step.
The CAL5000 was used as an independent means to rapidly and confidently determine the state of affairs. The CAL5000 includes both a 10 milli-ohm and a 1 milli-ohm resistance. By taking readings on the 1 milli-ohm and the 10 milli-ohm standards, the supervisor was able to determine his resistance bridge was out order.
This vital verification step did two things:
App Note: Verification of Calibration
Production line equipment verification is a required activity
for many production facilities. Historically this required
shipping expensive capital assets off-site. This can be a very
expensive and troubling process.
To mitigate this issue, the production manager at a large
electric motor production facility implemented the CAL5000 Calibration Verifications System. This allowed his onsite calibration technicians to perform the verification work within the framework of the quality management process.
The CAL5000 Calibration Verification System allowed the plant to keep its equipment up and running and reduce the effects of calibration related down time.
The reason is that the requirement for shipping the plant equipment off site is reduced, or even eliminated. This application of the CAL5000 Calibration Verification System was stated to provide return on investment in less than 1 year.
CAL5000S Surge Calibration/Spike Detection
User guide CAL5000S Rev 1
User Guide CAL5000 Rev 1: Implementation and specifications.
EDE Electric Motor Testing