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Fluke calibration 6331/7321/7341/7381 Deep-Well Compact Baths
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Personal Greeting

Find high temperature baths (300 °C) and refrigerated baths for low temperature calibration (–80 °C), in compact packages, and with deep immersion from Fluke Calibration our metrology baths are well known world-wide for excellent temperature control that maintains excellent temperature stability (±0.005 °C) and uniformity (±0.007 °C).

  • 457 mm (18 in) of depth with just 15.9 liters (4.2 gal) of fluid
  • Perfect for liquid-in-glass thermometers with optional LIG kit
  • Fast, quiet, compact (yet deep!), and economical

Need a bath with a lot of immersion depth, great stability, and a low price tag? How about one that minimizes fluid costs, changes temperatures quickly, and runs quietly?

Fluke Calibration's new Deep-Well Compact Bath series features four models covering temperatures from –80 °C to 300 °C.

Each model includes a 457 mm (18-inch) deep tank to accommodate long-stem PRTs, SPRTs, and liquid-in-glass (LIG) thermometers. Access openings are 120 by 172 mm (4.7 in by 6.8 in) so you can calibrate many thermometers simultaneously. Yet only 15.9 liters (4.2 gallons) of fluid are needed to get all the benefits Deep-Well Compact Baths offer.

Using our own best-in-class temperature controller, these baths deliver the performance you need for confidence in your calibrations. The 7381 (–80 °C to 110 °C) features both stability and uniformity better than ±0.007 °C over its entire range. The 7341 and 7321 (–45 °C to 150 °C and –20 °C to 150 °C, respectively) are stable to ±0.005 °C and uniform to ±0.007 °C at temperatures below ambient. And finally, the 6331 provides stability and uniformity from ±0.007 °C to ±0.025 °C over its range from 40 °C to 300 °C.

Be sure to understand the performance of the temperature calibration equipment you buy. Some manufacturers offer only limited (and often difficult to interpret) specifications. The specifications tab includes stability and uniformity values for the entire range of each bath—and tells you what fluid we used in the measurements. If that’s still not enough, give us a call and we’ll be happy to explain anything—and share data with you.

Fluke Calibration's control system automatically adds refrigeration when you need to cool down quickly, and shuts down refrigeration when you need to heat up quickly. For maximum stability, refrigeration levels are automatically balanced to match the set-point temperature you’re working at.

Connect any of these baths to a Fluke Calibration thermometer readout and our industry-leading MET/TEMP II temperature calibration software, and you’ll be performing automated probe calibrations within minutes from switch-on.

Want to optimize your bath for calibrating liquid-in-glass thermometers? Simple. With the optional LIG Thermometer Calibration Kit, you get an easy-to-install fluid level adapter tube that raises the meniscus of the bath fluid to within about 12 mm (0.5 in) of the top surface of the bath itself. The kit also includes a thermometer carousel that fits onto the top of the fluid level adapter tube and holds up to ten LIG thermometers in place. A magnifying scope (8X) is also available that mounts to the front of any Deep-Well Compact Bath so you can clearly see the liquid level of your thermometer against its temperature scale.

Like all Fluke Calibration baths, these units come with a report of test that includes one hour of stability data and a verification of set-point accuracy. A convenient overflow reservoir captures any excess fluid resulting from fluid expansion, allowing the trapped fluid to be reused following subsequent fluid contraction. A drain is also provided for easily emptying the bath’s tank when needed.

6331  35 °C to 300 °C
7321  –20 °C to 150 °C
7341  –45 °C to 150 °C
7381  –80 °C to 110 °C
6331 ±0.007 °C at 100 °C (oil 5012)
±0.010 °C at 200 °C (oil 5017)
±0.015 °C at 300 °C (oil 5017)
7321 ±0.005°C at –20°C (ethanol)
±0.005°C at 25°C (water)
±0.007°C at 150°C (oil 5012)
7341  ±0.005°C at –45°C (ethanol)
±0.005°C at 25°C (water)
±0.007°C at 150°C (oil 5012)
7381 ±0.006°C at –80°C (ethanol)
±0.005°C at 0°C (ethanol)
±0.005°C at 100°C (oil 5012)
6331 ±0.007 °C at 100 °C (oil 5012)
±0.017 °C at 200 °C (oil 5017)
±0.025 °C at 300 °C (oil 5017)
7321 ±0.007 °C at –20 °C (ethanol)
±0.00 7 °C at 2 5°C (water)
±0.010°C at 150 °C (oil 5012)
7341 ±0.007 °C at –45 °C (ethanol)
±0.007 °C at 25 °C (water)
±0.010 °C at 150 °C (oil 5012)
7381 ±0.007 °C at –80 °C (ethanol)
±0.007 °C at 0 °C (ethanol)
±0.007 °C at 100 °C (oil 5012)
Heating Time†
6331  130 minutes, from 40 °C to 300 °C (oil 5017)
7321  120 minutes, from 25 °C to 150 °C (oil 5012)
7341  120 minutes, from 25 °C to 150 °C (oil 5012)
7381  60 minutes, from 25 °C to 100 °C (oil 5012)
Cooling Time†
6331  14 hours, from 300 °C to 100 °C (oil 5017)
7321  110 minutes, from 25 °C to –20 °C (ethanol)
7341  130 minutes, from 25°C to –45°C (ethanol)
7381  210 minutes, from 25 °C to –80 °C (ethanol)
Stabilization Time
   15–20 minutes
Temperature Setting
   Digital display with push-button data entry
Set-Point Resolution
   0.01°; 0.00018° in high-resolution mode
Display Resolution
Digital Setting Accuracy
Digital Setting Repeatability
Access Opening
   120 x 172 mm (4.7 x 6.8 in)
   457 mm (18 in) without Liquid-in-Glass Thermometer Cal Kit
   482 mm (19 in) with Liquid-in-Glass Thermometer Cal Kit
Wetted Parts
   304 stainless steel
6331 115 VAC (±10 %), 50/60 Hz, 14.8 A or
230 VAC (±10 %), 50/60 Hz, 7.4 A, specify
7321 115 VAC (±10 %), 60 Hz, 14 A or
230 VAC (±10 %), 50 Hz, 7 A, specify
7341 115 VAC (±10 %), 60 Hz, 16 A or
230 VAC (±10 %), 50 Hz, 8 A, specify
7381 230 VAC (±10 %), 50 or 60 Hz, specify, 10 A
  15.9 liters (4.2 gal)
Size (HxWxD)
  1067 x 356 x 788 mm (940 mm from floor to tank access opening) [42 x 14 x 31 in (37 in from floor to tank access opening)]
6331  41 kg (90 lb.)
7321  62 kg (137 lb.)
7341  68 kg (150 lb.)
7381  91 kg (200 lb.)
   Use the 1586A Super-DAQ to automate temperature sensor calibration
   †Rated at nominal 115 V (or optional 230 V)
Model Name Description

Deep-Well Compact Bath, 40 °C to 300 °C


Deep-Well Compact Bath, –20 °C to 150 °C


Deep-Well Compact Bath, –45 °C to 150 °C


Deep-Well Compact Bath, –80 °C to 110 °C

Accessories common to all models:

Accessory Description
Calibration Bath Fluids

Full line of bath fluids

2019-DCB Fluid Level Adapter

Fluid Level Adapter

2069 Magnifying Scope

8X Magnifying Scope, with Mounts


IEEE-488 Interface, 6330/7320/7340


Spare Access Cover, Plastic, 7321, 7341, 7381


Spare Access Cover, Stainless Steel, 6331


TPW Holding Fixture (7321, 7341, 7381)


Mercury TP Holding Fixture (7341)


Spare Access Cover, Stainless Steel, 6331

Silver CarePlan

Fluke Calibration Silver CarePlans are available for most calibration products. Please contact your local Fluke Calibration sales representative for details or to request a quote. You may also call the Customer Care Center at 877-355-3225 or send email to careplans@flukecal.com.