5890 Micro Ohmmeter with temperature compensation.
The Type 5890 Micro ohmmeter is a true 4 terminal D.C. resistance measuring instrument. 

TYPE 5890 Basic ohmmeter
TYPE 5890C Ohmmeter with Comparator
TYPE 5890 Ohmmeter IE with IEEE-488
TYPE 5890 CIE with Comparator and 1EEE488
TYPE 5890 R with Recorder output 0-2 Volts

An additional facility now fitted to the 5890 is temperature compensation. A socket is fitted to the front panel to enable a 100 Ohm Platinum Resistance Thermometer to be connected when Temperature Compensation is required. Also included is a switch to select compensation for Copper or Aluminum. 

Seven ranges are selected by means of push button switches giving a maximum resistance range of 1900.0 Ohms down to 1 milli-Ohm with a resolution of 0.1 micro-Ohm on the lowest range. 
Another important feature of this instrument is that it incorporates automatic zeroing which is very important when measuring very low D.C. resistance.

Application

The Type 5890 Micro Ohmmeter has been designed for use where 4 terminal low resistance measurements are essential. Typical users are manufacturers of Cable, Wire, Switchgear, Electric Motors, Small Transformers and other applications where the accuracy and reliability of low resistance readings are of the utmost importance. 

Manual Zeroing

In this mode of operation the switch marked ZERO is depressed, this switches the current off through the object under test and any thermal E.M.F's present in the circuit are then balanced out automatically with zero indicated on the digital display. When the READ switch is operated the current is switched on and the true resistance value is indicated.

Auto Zeroing

When the AUTO ZERO switch is operated the instrument will display the reading of the object under test, and approximately every 10 seconds the zero is automatically updated. 
The resistance reading is frozen while the zero is being revalidated.

Fitted with Comparator

The comparator is a very useful option for batch measurement of components etc. 
The upper and lower limits can be set by means of thumb wheel switches. 
When the resistor under test is within the set limits a green L.E.D. is illuminated. 
Separate red L.E.D's indicate readings above or below the set limits. 
The comparator also incorporates relays thus enabling output signals to operate remote control devices. Connection to these relays is made via the back panel of the instrument.