Cognesense - Measure, Monitor, Protect

Cap Analog 421

The Cap Analog 421 is designed for process engineers, automation technicians, and plant operators who require accurate and stable level measurement with integrated control capabilities.

The transmitter delivers RF capacitance measurement precision combined with dual relay control flexibility in a single rugged instrument.

Unlike conventional transmitters that require separate controllers or frequent recalibration, the Cap Analog 421 integrates continuous analog output (4–20 mA or 0–10 V DC) with independent high and low relay outputs, temperature-stable electronics, and coating-rejection circuitry. This ensures reliable performance even with conductive, viscous, or sticky materials.

Designed for use with liquids, slurries, and bulk solids, the Cap Analog 421 provides fail-safe control, remote preamplifier capability, and explosion-proof construction. It is ideal for chemical plants, wastewater facilities, food processing operations, and bulk storage systems where both measurement and alarm control are required.

Cap Analog 421 RF Capacitance Level Transmitter

Applications

High and Low Level Control: Dual relays provide both high- and low-level functions within a single instrument, eliminating the need for multiple devices.
Viscous or Sticky Media: Coating-rejection circuitry maintains consistent accuracy in media that would normally cause signal drift in other sensing technologies.
Remote Tank Locations: Remote preamplifier design supports long-distance wiring without signal degradation, allowing calibration and monitoring from ground level.
Hazardous Environments: Explosion-proof housing and NEC approvals ensure safe and compliant operation in hazardous process environments.
Critical Pump Control: Dual setpoints and relay logic automatically manage pump-up or pump-down operations to prevent tank overfill or dry-run conditions.

Technical Specifications

Parameter

Description

Measurement Technology

RF capacitance with remote preamplifier and high-frequency excitation (~1 MHz)

Output Signal

4–20 mA DC and 0–10 V DC (standard); optional inverted output (20–4 mA or 10–0 V)

Relay Outputs

Dual SPDT relays (5 A at 115 VAC, 3 A at 230 VAC or 26 VDC non-inductive) with independent setpoints and adjustable differential

Power Supply

115 VAC (100–130 V) or 230 VAC (200–260 V), 50–60 Hz

Fail-Safe Modes

Selectable high or low level operation

Setpoint Range

0.08 into 200 ft water equivalent (0.5–30,000 pF adjustable)

Analog Accuracy

±0.1% of setting up to 1,000 pF

Temperature Stability

±0.01% per °F (±0.018% per °C)

Response Time

0.5 sec standard; optional adjustable delay from 50 ms to 10 sec

Operating Temperature

–40 °F to +160 °F (–40 °C to +71 °C)

Cable Length (Probe to Electronics)

Up to 1 mile (1.6 km) using shielded twisted pair

Probe Options

Rigid or flexible probes in 316 stainless steel, Teflon®, or Kynar® insulation

Housing

Explosion-proof cast aluminum enclosure

Enclosure Ratings

NEMA 4, 5, 7, 9, 12

Hazardous Area Approvals

NEC Class I Groups C and D; Class II Groups E, F, and G

Indicators

Red: Level ≥ setpoint; Yellow: Relay energized; Green: Probe/wiring OK

Accessories

AFI-150 / DFI-150 field indicators, remote calibration tools, and mounting kits

2026 COST ESTIMATE

Support

If you have a question that is not covered here, please contact the Cognesense support team for assistance.

What makes the Cap Analog 421 unique compared to other level transmitters?

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It combines continuous analog measurement with dual relay control in a single, explosion-proof device—reducing the need for separate instruments.

Can it handle buildup or coating on the probe?

Yes. Its coating-rejection circuitry compensates for conductive or sticky buildup, ensuring stable measurement accuracy.

How far can the electronics be mounted from the probe?

Up to 1 mile (1.6 km) using shielded twisted-pair cable, ideal for remote or inaccessible tanks.

How does the Cap Analog 421 support long-distance installation?

The Cap Analog 421 uses a two-piece design with an integral pre-amplifier at the probe head and a separate remote electronics unit. The pre-amplifier conditions the signal for long-distance transmission over a shielded twisted pair cable, allowing the main control unit to be installed up to 1 mile away in a safe, accessible location.

Is it suitable for hazardous areas?

Absolutely. The 421 is rated NEC Class I, Div 1 and Class II, Div 1, with explosion-proof housing and fail-safe relay modes.

Does it provide both alarms and analog output?

Yes. The 421 offers 4–20 mA or 0–10 V DC analog output alongside dual SPDT relays for high/low alarms or pump control.

What is the benefit of the dual relay outputs?

The dual SPDT relays allow the transmitter to perform basic process control in addition to continuous measurement. For instance, one relay can be set as a high-level alarm (shutdown) and the other as a low-level setpoint (pump-on), consolidating control logic and continuous signal output into a single instrument.

What industries commonly use the Cap Analog 421?

Common applications include chemical processing, wastewater treatment, food and beverage, and bulk storage systems where both measurement and alarm control are required.

Does the transmitter require frequent recalibration due to temperature changes?

No. The transmitter features temperature-stable electronics with a stability rating of 0.01% per °F. This high level of thermal compensation ensures that the analog output remains accurate and consistent, even in extreme outdoor or process temperature variations, minimizing the need for field recalibration.