About this module
The ZTM-ADC is built around the Analog Devices AD7124-8, a low-noise 24-bit sigma-delta ADC. It takes three floating thermocouples of any common type (B, E, J, K, N, R, S or T) and eight Pt1000 RTDs, and it is powered straight from its ZapLink port.
Each thermocouple goes to a floating differential input. The ADC's programmable gain amplifier (1 to 128) and internal 2.5 V reference suit thermocouple-level signals, and its bias voltage generator keeps floating probes centred. An on-board Pt1000 sensor provides the cold-junction temperature for compensation.
RTDs are measured ratiometrically against a precision 2 kΩ reference, so reference drift cancels out. The 500 µA excitation current is switchable, so it can be on only during a reading and avoid warming the probe you're trying to measure. Each input has a 100 Ω series protection resistor, which your readings need to allow for.
The ADC's burnout current sources make an open probe easy to spot, so it shows up as a broken wire rather than a surprisingly exciting temperature.
Used in these projects
- Cirrus 1 cloud chamber. Six RTDs map the temperature across the copper cold plate, and the thermocouples watch the chiller return and a TEC heat-sink.
- SonoLuma1 sonoluminescence (in development). Planned for liquid and cell temperatures.
KEY FEATURES
- 24-bit sigma-delta ADC (AD7124-8)
- 3 thermocouple inputs, types B, E, J, K, N, R, S, T
- On-board Pt1000 cold-junction sensor
- 8 Pt1000 RTD inputs, ratiometric
- Open-probe (burnout) detection
- Powered from ZapLink, no external supply
Supply
Powered from the ZapLink port
Thermocouples
3, types B, E, J, K, N, R, S, T
RTDs
8 × Pt1000, −250 to +850 °C
ADC
24-bit sigma-delta
Interface
ZapLink-SPI
