Description

Yokogawa AM25T 25-Channel Solid State Multiplexer

Configured for thermocouple channel expansion in Campbell Scientific data logger systems, the Yokogawa AM25T 25-Channel Solid State Multiplexer (AM25T Multiplexer) provides direct physical/electrical execution of multi-channel analog signal routing across Campbell Scientific data acquisition platforms.

Hardware Specifications

Parameter	Specification
ModelBrand	AM25T
Origin	USA
Weight	0.9 kg
Dimensions	23.6 x 5.1 x 13.2 cm
OperatingTemp	-40 degC to +85 degC
PowerConsumption	9.6 to 16 VDC, quiescent 0.5 mA, active 1.0 mA
Channel Capacity	25-channel solid state multiplexing
Expansion Limit	Up to 4 units per CR1000X/CR1000/CR3000, 3 per CR6, 2 per CR800/CR850
Switching Current	Max 25 mA
Relay Resistance	~500 ohm typical
Enable Logic	Inactive < 0.9 V, Active 3.5 to 5 V
Scan Clock	Falling edge triggered, min ON 50 us, OFF 60 us

Channel Multiplexing and Cold Junction Compensation Architecture

The AM25T implements solid state channel scanning with sequential activation controlled by external clock and enable lines from Campbell Scientific data loggers. Signal routing is performed through low-level voltage switching paths designed for thermocouple and millivolt sensor inputs. Internal PRT-based cold junction compensation is specified with accuracy of ±0.2 degC in the -25 to +50 degC range and ±0.4 degC in the -40 to +85 degC range, maintaining reference junction stability under varying enclosure conditions. The switching matrix is constrained by a 25 mA maximum per channel to prevent relay degradation and ensure long-term contact stability.

Frequently Asked Questions

Q: What is the maximum number of AM25T units supported per data logger?
A: Support varies by controller: up to 4 units for CR1000X/CR1000/CR3000, 3 units for CR6, and 2 units for CR800/CR850, based on sequential scanning constraints.

Q: What happens if switching current exceeds 25 mA?
A: Exceeding 25 mA can cause permanent damage to the internal solid state switching elements, resulting in degraded or non-functional channels.

Q: Is channel scanning simultaneous or sequential?
A: Channel activation is sequential, controlled by external clock pulses with falling-edge triggering logic.

Field Installation Guidelines

Mount the AM25T on a stable DIN rail or fixed enclosure backplate to minimize mechanical stress on terminal blocks. Maintain separation between thermocouple input wiring and power conductors to reduce noise coupling in low-level millivolt signals. Use twisted pair, shielded thermocouple extension wire and ground the shield at a single reference point to avoid ground loops. Ensure enable and clock signal lines remain within specified logic thresholds (0.9 V inactive, 3.5 to 5 V active). Do not exceed the 25 mA switching current limit on any channel path. Keep enclosure temperature within -40 degC to +85 degC operating limits.

Specifications

• Brand: Yokogawa

Advantages

• High reliability in industrial environments
• Supports continuous operation
• Compatible with major PLC/DCS systems