Time Electronics 1010 DC Voltage Calibrator - Manual (Page 6)

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1010 Technical Manual 6
2.3. Output noise
The electrical noise on the output voltage consists of chopper intermodulation, thermal noise
and random variations. Thermal noise becomes more significant on the lower ranges (see
Thermal EMFS). In general the total noise level is less than 20ppm of setting +/- 2 uV for the
10v, 1v and 100mV ranges over the frequency range 0 - 10 Hz and less than +/- 0.2uV (0-
10 Hz) for the lower ranges. Lower noise levels can be obtained by connecting a low pass
filter on the output terminals.
2.4. Common mode noise
Additional noise and variation of the output voltage can be caused by large common mode
voltages. These occur when the 1010 is used to calibrate (or measure) any input which is
above ground potential or has an a.c. component with respect to ground. When battery
powered, the 1010 has inherently a very high d.c. common mode rejection, but it is not
recommended that 100V d.c. common mode be exceeded. The a.c. common mode rejection
is determined by the capacitive unbalance to ground of the output terminals and associated
connections. The 1010 is checked before despatch with 30 Vp-p 50 Hz common mode
voltage on the output terminals.
2.5. Thermal emfs
When the 1010 is used to provide precision voltages of less than about 1 mV, care must be
exercised to avoid errors due to thermal emfs. These occur where temperature differences
are present at the junctions of dissimilar metals, e.g. a normal solder to copper junctions has
a thermal emf of approximately 3 uV/°C. Errors inside the 1010 under temperature stable
conditions are typically less than +/- 0.2uV.
2.6. Fuses
The power supply and output fuses are mounted on the INSIDE of the front panel printed
circuit board. Access is by removing the instrument front panel as described in Section 3.
Both are 20mm 250mA types. Spare fuses can be obtained directly from Time Electronics
Ltd, from your local supplier, or an authorised distributor.