Time Electronics User Manual
9780 Clamp Meter Adaptor v1.2
9780 Clamp Meter Adaptor Page 6 of 12
2.2 Principle of Operation
When a current passes through a cable it creates a magnetic field proportional to the
current. The clamp meter jaws measure this field. If the same wire (with the same current)
passes through the jaws again, the clamp meter will read double. If we pass 50 turns
through the jaws, the clamp meter will read 50 times (x50) the actual current passing through
the cable.
2.3 x1 and x50 Coils
The 9780 is fitted with 2 main coils. A single turn coil (x1) and a 50 turn coil (x50). The x50
turn coil can effectively multiply the current by a factor of 50, allowing current clamps to be
calibrated up to 1100 A.
2.4 Leads and Connections
The 9780 is supplied with a special set of high current connections leads. The binding post
screw cap on the 9780 must be fully removed and the ring terminal placed over the post.
Make sure the 9780 binding post screw caps are tight and the plugs are fully inserted into
the 7051 before performing any calibrations.
2.5 Duty Cycle and Heating
The 9780 is rated for continuous operation at 10 A. At 22 A the duty cycle (on/off time)
should be, a maximum of 3 minute on and 6 minutes off. When used with older style clamp
meters where substantial operating power is required it should be noted that additional
power will be required from the current source. If the clamp coils are too hot to touch, then
the current source should be removed until the coils have cooled. There is no chance of
electric shock from the coils.
2.6 Current Source
Not all calibrators have the required compliance voltage to drive the 9780 to its full rating.
It should also be noted that some clamp meters apply additional loading and the power
required to drive the 9780 is increased. In this situation the compliance voltage may not be
sufficient to drive the x50 coil to its full rating.
Immediately applying the maximum current to the 9780 may cause the output of the high
current source to trip. To avoid this, apply a lower current and slowly increase the high
current source until the desired current is reached.
For example, to reach 20 A, start at 18 A and increment the output in 0.1 A steps.
2.7 Jaws less than 20 mm Diameter
Some current clamps have very small jaws that will not fit around the coils. It is possible to
utilise one side of the coil, which provides 25 turns. If this method is used the connection is
made to the x50 terminal. If the jaws are less than 15 mm diameter it is possible to use a
single high current test lead (TE 9546 for example) connected to directly to the calibrator.
