Economical Thermal Flow Switch for Water-Based Liquids
The KOBOLD KAL is a temperature-compensating thermal flow switch that continuously monitors water-based liquid flow using the calorimetric principle — with no moving parts, extremely low pressure loss, and relay switching for flow and, optionally, temperature. A one-piece stainless steel sensor pairs with a remote controller, and the KAL is made in the USA.
The KOBOLD KAL series delivers cost-effective monitoring of water-based liquid flows in demanding industrial settings where minimal pressure drop and high reliability are essential. The one-piece stainless steel probe ensures durability under pressures up to 1450 PSIG (360 PSIG for models KAL-5132 and KAL-5140), and this versatile switch helps maintain process efficiency by indicating flow status without introducing significant head loss.
The KAL supports water-based liquids across pipe sizes from 1/4" to 20", with flow velocities ranging from 0.2 to 6.6 ft/s. This represents flow rates as small as 0.02 GPM in a 1/4" pipe up to 6,400 GPM in a 20" pipe.
How the KAL Works: Calorimetric Measurement Principle
The KAL operates on the established, time-proven calorimetric principle: a heated sensor in the flow stream is cooled by the moving liquid, and the electronics translate that cooling effect into a velocity-based flow reading. An internal microprocessor compensates for media temperature changes, so the switch point changes negligibly with temperature.
A resistance temperature detector (RTD) within the probe is heated several degrees above the liquid media temperature. As flow occurs, the moving liquid removes heat from the sensor, creating a proportional cooling effect that the integrated electronics measure to determine velocity. An internal microprocessor applies temperature compensation via a pre-loaded lookup table to eliminate setpoint drift from process variations. Full temperature compensation of the switch point is obtained through a simple, one-time calibration procedure.
The switch points are set via easily accessible potentiometers on the controller. Response times range from 5 to 12 seconds, making it suitable for real-time alarming. This design, rooted in heat transfer principles, delivers repeatable readings insensitive to dirt buildup, as the probe's flush surface avoids the fouling common in traditional paddle or float flow switches.
To learn more about thermal flow technology and its advantages and limitations, please visit our in-depth article about Thermal Flow Technology.
Sensors, Controllers, and Cable Options
The KAL is a two-part device consisting of a thermal sensor and a remote, rack-mounted controller. Sensors are available as insertion-style probes or installed in an integral T-piece for inline installations, and three controller series — KAL-E100, KAL-E200, and KAL-E300 — provide increasing levels of indication and switching capability.
The insertion-style fittings come in either 304 or 316 stainless steel, in 1/4", 1/2", and 3/4" NPT sizes. The inline version always comes with a 304 stainless steel sensor and either a brass or 304 stainless steel T-piece housing, covering 1/4" through 1-1/2" NPT connections.
According to specifications, the KAL-E100 provides a flow-rate-sensitive, isolated SPDT relay with a green LED status indicator and is offered with a 24 VDC supply (KAL-E130). The KAL-E200 adds an LED trend indicator for flow rate and switch point, and the KAL-E300 includes an additional SPDT relay for temperature monitoring, with an alarm temperature settable up to 176°F (80°C). All sensor models are compatible with all three controllers.
The sensors come standard with 6-foot PVC cables (silicone optional) but can be extended for controller locations up to 330 feet away. Sensors and controllers are both available with a high-temperature option supporting media from 32 to 250°F (0 to 121°C).
Key Features and Performance Advantages
Designed to handle challenging environments with low maintenance needs, the KAL combines an IP68-rated probe with remote electronics in a polycarbonate, IP40-rated housing that mounts on standard DIN rail for quick panel integration. Fail-safe relay logic and long-term memory retention are engineered to protect the monitored process even when power is interrupted.
- No moving parts for extended service life and reduced risk of mechanical failure
- Extremely low pressure loss to preserve system efficiency
- Simultaneous flow and temperature monitoring with optional second relay output
- Insensitive to particulates in water-based media
- Trend LED indicator on select models for quick visual status of flow versus setpoint
- Fail-safe operation: relay energizes normally, with 10-year memory retention on power loss
- Temperature compensation via controller microprocessor enables negligible setpoint shifts due to media temperature changes
- Simple potentiometer adjustment for switching points
Common Questions about KAL - Temperature-Compensating Thermal Flow Switch for Water-Based Liquids
The measuring probe is heated a few degrees warmer than the medium surrounding it. When liquid moves past, it carries that heat away and the probe cools; the degree of cooling represents the flow velocity. The electronic setting system compares the desired flow speed with the actual speed and activates the output relay when the set value is not reached.
Published water ranges span nominal inside diameters from 1/4 inch through 20 inches — 0.02 to 1.0 GPM at the smallest size and 130 to 6,400 GPM at the largest, according to specifications. Because velocity varies across a pipe's cross-section, probe insertion depth, internal diameter, and flow profile can produce deviations from these calculated ranges.
The sensor is rated for operating pressures to 1450 PSIG, while models KAL-5132 and KAL-5140 carry a 360 PSIG limit. Standard media temperature reaches 176°F (80°C); the "..HT" high-temperature option shifts the range to 32 to 250°F (0 to 121°C). The controller itself is rated for ambient temperatures to 176°F, according to specifications.
All three series mount in a standard DIN housing and switch through fail-safe SPDT relays. The base KAL-E100 signals a flow switch point only and is supplied for 24 VDC as the KAL-E130. The E200 series adds a trend display showing flow rate against the set point, and the E300 series also monitors temperature through a second relay.
A 6-foot (1.8 m) PVC-clad cable is standard, with silicone available as an option. The connecting cable between the sensor and the controller may run as long as 330 feet (100 m). With KAL-E300 series units, a temperature-correction step is required when cable length exceeds 33 feet (10 m).
No — the sensor functions in any fitting position, provided the pipe remains completely filled with the liquid being monitored. Choose a location free of turbulence, allowing four pipe sections upstream and downstream of the probe. During zero-point calibration, flow must be at zero and no air bubbles may be present on the sensor.
The relay is held energized during normal operation, so an alarm is signaled whenever it releases — on power failure, line break, short circuit, or flow falling below the desired value. Configuration settings are retained for 10 years without power, and LEDs on the controller indicate relay and power status.
Display accuracy is ±10%, with ±2% repeatability and ±2% temperature accuracy, according to specifications. Response time typically runs 5 to 12 seconds. End users can adapt the equipment to their unique installations through a one-time calibration, which keeps the switch point stable as the process liquid's temperature varies.
None on a routine basis — the device itself requires no maintenance. KOBOLD recommends checking the sensor at monthly intervals for deposits such as lime scale and cleaning it where necessary. With proper installation, the probe shows no sensitivity to soiling and causes practically no pressure loss in the line.
Product Specifications
Switching Range
0.2...6.6 ft/s
Flow Range
0.02...1.0 to 130...6,400 GPM
Fittings
1/4"...1-1/2" NPT Thread
Max. Temperature
176 (80 °C) /250 °F (120 °C)
Output
Relay Outputs for Flow and Temperature Monitoring
Product Features
Remote Probe Allows Installation with Minimal Clearance
Can be Used with Low or High Flow Velocities
Extremely Low Pressure Loss
Simultaneous Monitoring of Temperature and Flow
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