Seaward RH9A Series - Manual (Page 11)

8
RH9A Series High Resistance Decade Boxes Operating Instructions
Routine Maintenance
With normal usage the RH9A requires little or no
maintenance. The special insulators around the High and
Low input sockets should be kept clean to avoid the
shunting effect of accumulated dirt and grease. Wiping
with an alcohol moistened cloth should be suffi cient to
maintain accuracy.
If the instrument is removed from its case for any reason,
the resistors must never be touched with the fi ngers.
Touching the resistors will seriously effect the calibration
of the instrument and may cause progressive
deterioration of accuracy.
Calibration of the RH9A requires a Precision
Terraohmmeter and a Resistance Bridge such as a
Wheatstone or a Comparator Bridge with another RH9A
with known calibration for comparison.
Replacement of individual resistors is not recommended
as resistors are selected and matched by Cropico as part
of each decade to maintain the specifi ed accuracy
throughout the entire resistance range.
Should switch lubrication ever be required, only a pure
silicone lubricant should be applied very sparingly.
Ordinary switch lubricants may have a low leakage
resistance, which will change the calibration of the higher
resistance decades.