Time Electronics 1048 Voltage-Current-Loop Calibrator - Manual (Page 6)

6
V1.2 30/12/10 P a g e | 6 1048 Technical Manual
3.
Normal Operating Mode
3.1.1. Resolution high/low
The unit has a unique method of changing the display resolution when values greater than
the conventional 19999 (4.5 digit) display are used. This feature allows the units ranges to
be extended by 10% above the commonly used 0.2/2.0/20 full scales. Calibration of values
just above these figures is now possible. This will be found particularly useful with 4 - 20mA
transducers where they are slightly over scale but are still within specification.
For both measure and source functions, high resolution (4.5 digit, e.g. 1.9999) will apply for
all values below:
• 0.20 on the 0.22 range
• 2.0 on the 2.2 range
• 20 on the 22 range
All values above those above will be displayed to 3.5 digit resolution e.g. 21.05.
The change-over from high to low resolution is automatic. However, if the value increases
and the resolution changes from high to low, it will not return to high resolution until the
value is reduced to:
• 0.1on the 0.22 range
• 1.0 on the 2.2 range
• 10 on the 22 range
To force the display back into high resolution the output polarity switch, should be operated
from Hi to Lo to Hi. There is a marking on the front panel below the switch to indicate this.
3.1.2. Output polarity switch
It is important for the user to understand the operation of the output polarity switch (‘F’ on
the front panel diagram section 2.). The switch has three positions, NORM/OFF/REV, and
its function depends on the operating mode being used.
Measure function (V & mA)
In the NORM position the unit will measure inputs connected in the same polarity as the
terminals i.e. red is positive and black negative.
The OFF (centre) position, when measuring voltage, disconnects the signal internally and
leaves the input terminals still providing 1M ohm input resistance. The display should read
zero but occasionally the last digit may show ‘1’, this is normal and is within the
specification.
The OFF position, when measuring current, disconnects the signal internally and leaves the
input terminals still providing the current shunt input resistance. The display should read
zero but occasionally the last digit may show ‘1’, this is normal and is within the
specification.
The REV position is not used since the unit’s measuring capability is bi-polar i.e. it can
accept both +ve and –ve input signals. The –ve inputs are displayed with a ’-’ sign in front of
the value.