These Resistance Standards are primarily designed for use with altering currents at power frequencies. They are equally suitable for use from d.c. to 1 kHz. The range of resistors available is from 0.0001 Ohm to 10,000 Ohms. For constructional reasons these resistors have been divided into four groups. The units of each group are of similar mechanical design and dimensions which have been determined with consideration for a common upper limit for heat dissipation and current carrying capability.
The resistance material is manganin (Cu-Ni-Mn alloy). The resistors are built into cylindrical metal containers for oil immersion to ensure uniformity of temperature, the 10 and 50 watt units are air cooled and fitted with a hand operated mechanical oil stirrer. The 200 Watt units are water cooled and provided with a pulley to drive the mechanical oil stirrer.
The terminal arrangements provide for separate current and potential terminals for use with a potentiometer or DVM. The available standard ranges and electrical performance data are set out in Table below. Modified resistance units can be quoted to meet special requirements.
N.B. - These standards are not filled with oil when supplied. The recommended oil is Castrol Whitemor WOM14 or if not obtainable any high quality non- corrosive oil can be used such as high quality Transformer Oil.
