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Cap Analog 421

RF Capacitance Level Transmitter

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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 420
Cap Analog 421 RF Capacitance Level Transmitter
Cap Analog 421

Features

Stable RF Capacitance Sensing

High-frequency excitation ensures drift-free measurement across conductive and non-conductive media, maintaining accuracy despite product variability or changing process conditions.

Integrated Analog and Relay Outputs

Provides continuous level transmission plus dual independent relay setpoints for alarms or pump control, reducing hardware requirements and simplifying system architecture.

Independent Calibration Controls

Zero, span, and setpoint adjustments are non-interactive, enabling fast, precise field calibration without signal interaction or long-term drift.

Selectable Fail-Safe Modes

High or low fail-safe settings de-energize relays on power loss or wiring faults, enhancing operational safety for tanks and pumps.

Coating-Rejection Circuitry

Compensates for conductive or sticky buildup on the probe surface, allowing consistent measurements without frequent probe cleaning or recalibration.

Long-Distance Remote Mounting

Preamplifier and twisted-pair design support probe-to-electronics distances up to one mile, enabling safe access from ground level in remote tanks.

Applications

  • High/Low Level Control: Dual relays provide independent high and low alarms, enabling pump sequencing, overfill protection, or dry-run prevention in one instrument.
  • Viscous or Sticky Media: Coating-rejection circuitry maintains stable readings when product buildup or conductive films accumulate on the probe surface.
  • Remote Tank Locations: Long cable capability supports installation where tanks are tall, buried, or inaccessible, allowing calibration from ground-level control areas.
  • Hazardous-Area Storage: Explosion-proof housing ensures safe operation in flammable or dusty environments, meeting NEC requirements for industrial classified locations.
  • Critical Pump Automation: Independent relay setpoints manage pump-up or pump-down logic accurately, reducing risk of overflow, equipment damage, or unplanned outages.
  • Bulk Solids Handling: RF capacitance provides reliable level switching in powders, grains, plastics, and other dry materials unaffected by dust clouds or aeration.
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Specifications

Measurement Technology

RF Capacitance, remote preamplifier with high-frequency excitation (≈1 MHz)

Output Signal

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

Relay Outputs

Adjustable differential and independent setpoints

Power Supply

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

Fail-Safe Modes

Selectable High or Low level (relay de-energized above or below setpoint)

Setpoint Range

0.08 inch to 200 ft of water equivalent (0.5–30,000 pF field adjustable)

Analog Accuracy

±0.1% of setting up to 1,000 pF

Temperature Stability

±0.01%/°F (±0.018%/°C)

Response Time

0.5 second standard; optional 50 ms–10 sec adjustable delay

Operating Temperature

–40 °F to +160 °F (–40 °C to +71 °C) for both preamp and remote amplifier

Cable Length (Probe to Electronics)

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

Probe Options

Rigid or flexible designs in 316 SS, Teflon®, or Kynar® insulation

Housing

Explosion-proof cast aluminum, NEMA 4, 5, 7, 9, 12

Enclosure Approvals

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

Indicators

  • Red LED: Level at or above setpoint
  • Yellow LED: Relay energized
  • Green LED: Probe and wiring OK (diagnostic)

Accessories

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

Contact Support
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Contact Support

If you have questions not covered here, please contact the Cognesense support team for assistance.

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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?

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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?

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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?

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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?

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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?

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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?

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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?

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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?

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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.

Summary

For more than a century, Cognesense has combined precision, reliability, and safety in process instrumentation. The Cap Analog 421 extends this tradition with a powerful blend of analog level transmission and dual relay control in one rugged package.

Designed for challenging applications in chemical, food, wastewater, and bulk liquid storage, the 421 delivers dependable accuracy, built-in safety, and maintenance-free operation.

Whether managing pump control, high/low alarms, or continuous monitoring, the Cap Analog 421 provides the performance and durability expected from an industry leader measurement instrumentation.

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