Question:
Can the DC1000 damage an LCR meter that is being used with the DC1000 during testing?
Answer:
When measurements are being made, the LCR meter and the DC1000 are in parallel and the voltage across the terminals and the DC1000 are exactly the same.
The voltage is the programmed LCR meter AC signal, for example 1V @ 20kHz, plus the DC voltage developed across the part under test by the DC1000 constant current output.
The DC voltage is also relatively small because the DC resistance of the part under test is usually small. For example, 10 amps DC current flowing through a 50mOhm winding will mean that a 500mV DC voltage is present.
The DC1000, with its unique electronic inductor configuration, will have an exceptionally low effect on the LCR meter output and measurement.
The effect upon the measurement accuracy is much smaller than the effect observed when using traditional dc bias supplies that are all built with large physical inductors.
There is definitely no ill effect on the LCR meter during normal use.
As with all high dc current testing of inductors there is the possibility of dangerous high voltages being present if the DC current connection is broken in the middle of a test.
If the inductor under test is energized by a high DC current and the current path is suddenly removed then the inductor will produce a large "back emf" according to Faraday's law.
The voltage generated may be dangerously high, hundreds or thousands of volts may be present for a short duration.
This is true for any design of ANY DC bias supply.
In this case, most often caused by accidental dis-connection of the DC supply during a measurement, both the operator and the equipment must be protected from damage.
In a production or "routine test" environment both the operator and the equipment are protected from high voltage by the use of the safety interlock facility of the DC1000. When correctly installed, a safety system ensures that the test connections remain untouched when a test is active.
Should the operator's hand move near the part under test, the DC bias current is removed safely and automatically such that no dangerous high voltage will be present.
This is the optimum protection method for production test.
In a design environment, with measurements being made by qualified engineers, it is not always possible to use a safety interlock system. In this case, it is good engineering to take further precautions against accidental misconnection.
The DC1000 contains over-voltage protection circuits that guarantee instrument and operator safety for devices that remain connected across both its output terminals.
This means that as long as the LCR meter terminals remain connected to the DC1000 terminals the DC1000 over voltage protection will ensure that no voltage over approximately 10V is present across the LCR meter.
There is the possibility of a dangerous voltage being applied to the LCR meter, but only if two items are true:
1. The DC bias current connection is removed abruptly during a test, when the dc current is 'on'.
AND
2. The LCR meter is connected separately (not via the DC1000 leads) to the part under test.
To avoid this possibility, connect the LCR meter to the DC Bias output securely and use only 1 set of connectors to connect to the part under test.
This is essentially the method used by other manufacturers since the LCR meter is connected via the bias supply.
As with all LCR meters, always perform open and short-circuit compensation before attempting reference measurements.
Short circuit errors will be small since, because the part under test is for high current, its connection impedance will be very small (when doing compensation of the LCR meter / DC1000 ensure that the DC1000 is ON and dial 0A for the set current).
In summary, the DC1000 DC current bias supply has a significantly smaller effect on the LCR meter measurements than other physical inductor type supplies.
The DC1000 user manual specifies error current as a function of applied ac test voltage (mA/A) and the user manual contains a graph of error current vs. test voltage.
For testing with ANY manufacturers DC bias supplies, good safety and engineering practice should be applied.
* A safety interlock system should be used for production testing by unskilled operators.
* Avoid the possibility of the DC current being removed with the LCR meter still being connected.
Do this by making secure connections between DC bias output and the LCR meter terminals.
Always compensate the measurement against the effect of stray short and open circuit impedances