SNAP Analog Input Modules

Opto 22 • 43044 Business Park Drive • Temecula, CA 92590-3614 • www.opto22.com

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14

Thermistor Input Module 0–400 K, 0–200 K,

0–100 K, 0–50 K, 0–40 K, 0–20 K, 0–10 K,

0–5 K, 0–4 K, 0–2 K, 0–1 K, 0–500 Ohm

SNAP-AIR400K-8

IMPORTANT: The mounting rack connector has 24 pins; the module

connector has 20 pins. The extra pins on the mounting rack

connector prevent misalignment of the module during installation.

Description

The SNAP-AIR400K-8 module has eight channels of analog to

digital conversion that convert resistance to temperature or to

Ohms. The module is ideal for NTC thermisters commonly used

in HVAC, refrigeration, and process control applications. It may

also be used with PTC thermisters in resistance sensing

applications. See the table on page 3 for I/O processor

compatibility.

NTC thermistor

Variable resistance device

Part Number

Description

SNAP-AIR400K-8

Eight channel analog resistor/thermistor

input, 400 K Ohms, 200 K Ohms,

100 K Ohms, 50 K Ohms, 40 K Ohms,

20 K Ohms, 10 K Ohms, 5 K Ohms,

4 K Ohms, 2 K Ohms, 1 K Ohms, 500 Ohms

The SNAP-AIR400K-8 reads variable resistance type

transducers, and it has 12 resistance input ranges from 500

Ohms to 400 K Ohms, plus Autorange. Range dependent

resolution is from 20 milliOhms to 16 Ohms.

SNAP PAC brains and PAC Control provide direct temperature

readings for four popular thermistors using the Steinhart-Hart

equation (see page 16). You may also enter custom

coefficients for unsupported thermistor curves.

The simple two-wire connections are made to the pluggable

terminal strip on top of the module.

NOTE: The eight input channels must be electrically isolated from

each other and earth ground. The transducer resistor element

must be isolated from any electrically conducting probe tube

housing.

See page 15 for module specifications.

Wiring Information

Unshielded 24 AWG wire (minimum) is recommended.