Keysight (formerly Agilent T&M) 44422A Relay Multiplexer

The HP 44422A is a plug-in assembly (Option 020) for the HP 3497A data acquisition/control unit. The 44422A is a relay multiplexer assembly with thermocouple compensation.The relay multiplexer assembly with thermocouple compensation can be used for voltage, termperature, and resistance measurements, but is primarily used with thermocouples for termperature measurements. The assembly consists of a relay card and a terminal card. The terminal card, which can be disconnected from the relay card, has temperature compensation circuits for thermocouple measurements.The 44422A assembly uses a special isothermal connector block on the terminal card to eliminate unwanted measurement errors when measuring thermocouple voltages.

Both hardware and software thermocouple compensation techniques are available. The 3497A does not directly measure temperature; rather, it measures voltage generated by thermocouples, which is proportional temperature and which can be converted to an equivalent temperature. However, the voltage measured by the 3497A is different to the actual thermocouple voltage uless some compensating technique is used. Hardware compensation can be used to measure the inputs of up to 20 thermocouples per assembly, but it is limited to one thermocouple type per assembly. Software compensation can be used to measure the ouputs of up to 19 thermocouples, with any mixture of thermocouples.

Key Features

• Compatible thermocouples
  • Software: Any mixture
  • Hardware: One of B, E, J, K, R, S, T
• Measurement channels available per assemblyReference junction compensation accuracy: 1°C
  • Software: 19
  • Hardware: 20
• Maximum input voltage: <170 Vp between any two input terminals
• Maximum current: 50 mA per channel non-inductive
• Maximum power: a VA per channel
• Thermal offset
  • Direct switched: <1 µV differential
  • Tree switched: <2 µV differential
• Closed channel resistance
  • In series: 100 Ω ±10% in High, Lo, and Guard
  • Relays contacts only: <1 Ω per contact