The Dranetz 658 Power Analyser current clamp inputs are designed to convert current supplied from a current clamp on the input to voltage. This is done with the aid of a 120W resistor.
Popular current clamps intended for use with standard multimeters (e.g. Chauvin Arnoux) have the current to voltage conversion built in with typical full scale voltages of 1V. These are thus unsuited to the 658. Converting the current clamp is sometimes possible, but this would render them only useful for the 658.
Also, with the 658, the input resistor is often reported to be damaged with over-current on the current clamp. This renders the input channel useless until the unit is repaired.
The following is a modification to bring the 658 in line with the industry standard 1V making it suitable for use with a range of clamps within the PQ industry (with the added advantage that should a current clamp be damaged by over current, the 658 is still functional). The converted input suits my favourite, the Chauvin Arnoux 173, a switchable 1-10-100-1000A:1V clamp.There are two notes:
Above is the circuit of the unmodified current input amplifier/buffer. The current-to-voltage conversion centres around R82, a 120W resistor. The full scale input current is 12.2mA which translates to 1.465Vrms (as tested on all 3 channels of my 658).
Modifying the 658 is extremely simple and centres around R82 only. The input impedance decided on was the industry standard of 1MW.
While consulting the inset photo, the steps are:
This completes the circuit seen above, a 2.048:1 voltage divider and creates an input full scale of 1.465 x 2.048 = 3Vrms.
The 5A scale is unused from this point on (unless you are prepared to permanently divide the result by 1.66!).
The input full scale is now 3V for 30, 300, or 3000A as set on the Main Channel Setups, which represents 1V for 10, 100, and 1000A and thereby matches a majority of industry available PQ clamps.
If there are any questions please ask.
Note: This web page does not form part of any official documentation.
© M.T.P. - 25.02.04