Hypatia Model 307 Performance Verification Procedure Version 3.1
15 November 1993 © 1989-1993 Hypatia Inc.
Potentially lethal line voltages of as much as 132 Volts rms are present
on exposed terminals within this instrument. Opening the instrument cabinet
is not necessary and is not recommended for the performance verification
procedure. If repair service is required but you are unfamiliar with the
precautions and techniques necessary for servicing instruments with exposed
line voltages, do not attempt to service the instrument yourself. Instead,
refer service to appropriately experienced technicians.
Warning: This instrument produces exposed high currents as a normal part of its function. High current shorts through rings, wrist bands or other conductive apparel can cause serious thermal burns which may result in permanent injury. Operators are advised to remove all conductive apparel, especially from the hands and wrists, prior to any operation or service of this instrument.
There are no adjustments within this instrument. There is no need to open the cabinet to perform a performance verification. If the instrument fails any performance verification step, replacement of the associated components or cleaning of the instrument will be required. Nine internal test points are provided to facilitate localization of accuracy deficient circuit areas or other malfunctions. Contact Hypatia for service documentation.
Model 109 Kelvin sense probes are required. (If unavailable, they can be easily built: Terminate four conductor telephone type flat cable with a telephone type modular connector on one end and solder all four conductors to a small alligator clip on the other end. A 1.5 meter length is suggested for each probe, but not required.) Two alligator clip probes (Model 101 or 105) are recommended, but are not required so long as a stout means of attaching two Model 100 series power probes to a power resistor bank and the 100 milliohm cabinet mounted check resistor can be achieved.
Test Instruments and Fixtures:
One rms voltmeter with at least .2% accuracy and at least 1 mV resolution.
One digital counter with at least .2% accuracy and at least .1 Hz resolution. An extended averaging time may be required.
One precision power resistor bank, with sense connection points, totaling at least 100 milliohm with at least .2% accuracy, and with taps if verification at readings of less than 100 milliohm are desired. This resistor bank must have a current handling capacity at least meeting the capacity and duty cycle limits of the Model 307.
1. Set the Model 307 "main power" and "test current" switches to the off position. Rotate the "current adjust" control knob to its full counter clockwise position.
2. Connect an IEC power cord to the rear panel IEC receptacle of the Model 307 and to a power source meeting the specifications printed above the IEC receptacle.
3. Set the Model 307 "main power" switch to the on position and allow five minutes to establish near thermal equilibrium.
4. Secure two Model 100 series power probes, preferably alligator clip types (Model 101 or 105), to the front panel connectors of the instrument as described in the operation section of the manual, but leave the modular connectors unconnected. Connect the Kelvin sense probes (Model 109) to the modular receptacles. Connect the power probe ends to a 100 milliohm precision power load. Connect the Kelvin sense probe ends to the sense taps of the precision load, being certain that the right Kelvin sense line is connected to the same side of the load as the right power probe, and similarly for the left sense line and probe. Verify that the Kelvin connectors do not directly physically touch the power probe connectors.
5. Set the "timed test / continuous test" button to the continuous test position. Set the "meter mode" button to the milliohm position.
6. Set the "test current" switch to the on position and slowly increase the test current to 10 Amps. Record the Model 307 impedance reading. Repeat for 17.5, 25, 30 and 50 Amps. Perform the 50 Amp test quickly so as not to violate duty cycle limits. Complete these tests by setting the "test current" switch to the off position and rotating the "current adjust" control knob to its full counter clockwise position. Compare the results to specifications.
7. If impedance measurement performance checks for load values other than 100 milliohm are desired, repeat step six for each value.
8. If altered, return the load bank to 100 milliohm. Connect an rms voltmeter to the sense taps of the precision load. Set the "meter mode" button to the current position.
9. Set the "test current" switch to the on position and slowly increase the test current until the rms voltmeter reads 1.00 volts, which equates to 10.0 Amps. Record the Model 307 digital current reading (current meter accuracy). Then vary the current adjust control so that the Model 307 bar graph flickers between 7.5 and 10 Amps. Record the rms voltmeter reading (bar graph accuracy). Repeat for 17.5, 25, 30 and 50 Amps. Perform the 50 Amp test quickly so as not to violate duty cycle limits. Complete these tests by setting the "test current" switch to the off position and rotating the "current adjust" control knob to its full counter clockwise position. Compare the results to specifications.
10. Set the "meter mode" button back to the milliohm position. Establish a connection between the probe's measurement ends and the 100 milliohm check resistor on the back of the instrument. Use the Kelvin sense lines, being certain that the right Kelvin sense line is connected to the same side of the 100 milliohm resistor as the right power probe, and similarly for the left sense line and probe. Verify that the Kelvin connectors do not directly physically touch the power probe connectors.
11. Turn the "test current" switch on and rotate the "current adjust" knob clockwise until a current of 17.5 Amps is reached. Record the impedance reading and compare to the Model 307's reading of the 100 milliohm precision load taken earlier at 17.5 Amps to determine the value of the cabinet mounted check resistor by error subtraction. The result should be 100 milliohm ± 1%. Rotate the "current adjust" knob to its full counter clockwise position, but leave the "test current" switch on and probes in place for step 12.
12. Proceeding directly from step 11, push the "> 100 milliohm alarm" button to it's on position. Rotate the "current adjust" knob clockwise until a current of about 10 Amps is reached. If the impedance reading is 100.0 milliohm or higher, the audio alarm should sound, but if less than 100 milliohm, it should not sound. Rotate the "current adjust" knob in alternate directions to vary the test current between 0 and 17.5 amps. This will cause transient impedance reading variations above and below 100 milliohm. Check that the alarm sounds for readings above 100 milliohm and is silent for readings below 100 milliohm. Complete this test by setting the "test current" switch to the off position and rotating the "current adjust" control knob to its full counter clockwise position.
13. Remove all of the probes except the left Kelvin sense probe from the Model 307. Carefully remove the "timed test / continuous test" button from its shaft by pulling it straight out from the face of the instrument. If you're unable to do this by pulling with your fingers, use a light pair of pliers with rubber barrier jaws or equivalent to protect the plastic button from damage.
14. Connect the reference terminal of a digital counter to the alligator clip end of the left Kelvin sense probe. Clip the high lead of the counter to the metal stop plate on the shaft of the "timed test / continuous test" button (about 4 mm behind the front panel). This plate is connected to a 10 Hz signal derived from the internal time base.
15. Verify a reading of 10.0 Hz ± 1%. If your reading is outside specs, set your counter to average over a longer period if possible and recheck, or use an oscilloscope with a calibrated time interval measurement capability. This clock signal is not symmetrical - it includes pulse blanking which may cause misreadings on some counters if averaging times are too short. A typical correct reading is 10.00 Hz. A typical misreading due to counter aliasing is 9.84 Hz. Replace the button to complete this test.
16. Set the "power" switch to the off position and remove the left Kelvin sense probe and the power cord from the instrument.
17. Check that the two lower rear #15 torx screws which secure the top
cabinet half are tight and that there is a lockwasher located between the
cabinet halves on these screws to insure proper grounding of the upper cabinet
half. The edges of the lockwashers are visible from the bottom of the instrument.
This Completes the Performance Verification Procedure.
© 1989-1993 Hypatia Inc.