GE DS3820CI2AD21C

Key Parameters

• Channels: 2 independent counter/encoder inputs

• Input Type: 24 V DC, differential or single-ended (software-configurable per channel)

• Maximum Input Frequency: 100 kHz per channel (with filter disabled)

• Resolution: 32-bit counter per channel

• Count Modes: Up/down counting, quadrature x1/x2/x4, frequency measurement, period measurement, pulse-width measurement

• Input Filtering: Software-selectable 0.1–10 ms debounce

• Differential Inputs: RS-422 compatible (A+, A-, B+, B-, Z+, Z-) for noise-immune long-distance encoder connections

• Isolation: 1500 V RMS (field-to-backplane); 500 V RMS between channels

• Terminal Type: 21-pin screw-type (per suffix “D21C”)

• Diagnostics: Per-channel LED status, over-range detection, count-lost detection

• Power: 24 V DC backplane power, ≤2.5 W (plus external field supply)

• Operating Temperature: –40°C to +70°C

Advantages

• Differential inputs – provides superior noise immunity for long cable runs (up to 100 m); rejects common-mode noise common in VFD-heavy environments.

• Dual high-speed counters – two independent 100 kHz channels in one slot; saves rack space.

• Versatile measurement modes – supports counting, quadrature decoding, frequency, period, and pulse-width – all in one module.

• Quadrature x4 decoding – delivers 4× resolution from standard incremental encoders.

• Flexible input configuration – each channel independently set for differential (RS-422) or single-ended (24 V DC) input.

• Index/Z-input support – allows homing and position reset for absolute referencing.

• Adjustable input filtering – eliminates false counts from contact bounce and noise.

• Hot-swappable – replace without rack power-down.

Applications

• Position feedback – reading incremental encoders on servo motors, conveyors, and positioning tables in high-EMI environments

• Flow measurement – counting pulses from turbine flowmeters with long cable runs

• Speed monitoring – frequency measurement from proximity sensors on rotating shafts in motor control centers

• Web handling – tension control and registration with encoder feedback

• Packaging machinery – product counting and cut-to-length positioning

• Printing presses – registration control with quadrature encoders

• Wind turbines – speed and position monitoring with long cable runs from nacelle to controller

Competitor Comparison

The DS3820CI2AD21C is the differential-input variant, offering significantly better noise immunity and longer cable support than the single-ended DS3820CI2A. Compared to competitor differential-only modules, the DS3820CI2AD21C adds the flexibility of software-configurable single-ended mode, allowing it to work with both differential encoders and standard 24 V proximity sensors. Against competitor modules that only support counting, the DS3820CI2AD21C offers frequency, period, and pulse-width measurement – a broader feature set for the same price. For applications with cable runs exceeding 30 m or high-EMI environments, the DS3820CI2AD21C is the essential choice.

Selection Tips

• Choose DS3820CI2AD21C when your encoder cables exceed 30 m or when operating in high-EMI environments (VFDs, welding, substations).

• Ideal for differential encoders (RS-422 output) – the DS3820CI2AD21C supports A+, A-, B+, B-, Z+, Z- inputs.

• Can also be configured for single-ended 24 V DC sensors – making it versatile for mixed systems.

• Verify encoder output type and voltage – the differential inputs accept RS-422 levels (±5 V) as well as 24 V single-ended.

• Confirm the terminal configuration (D21C screw-type) matches your panel wiring requirements.

• Not suitable for 5 V TTL encoders without external level shifting.

Precautions

• Differential wiring: Use twisted-pair shielded cables for each differential pair (A+/A-, B+/B-, Z+/Z-). Maintain proper cable twist to maximize noise rejection.

• Cable length: For differential mode, the DS3820CI2AD21C supports up to 100 m with proper shielding; beyond this, signal degradation may occur.

• Termination: If using single-ended mode, connect the unused differential input (-) to the common ground of the sensor to avoid floating inputs.

• Frequency limits: Maximum 100 kHz achieved only with filtering disabled. Enable filtering only if necessary.

• Power: The DS3820CI2AD21C requires external 24 V field power for sensor/encoder excitation – ensure power supply capacity for encoder current draw.

• Shielding: Ground shield at module end only to avoid ground loops.

• Configuration: Set differential/single-ended mode before operation – changing modes during runtime may cause count errors.

• Spare: Keep one spare DS3820CI2AD21C for critical position or flow loops – differential modules are subject to field wiring faults and surge damage.