Catalogs > Industrial Controls Catalog > Condition Sensing Switches and Controls > Temperature, Mechanical
Temperature, Mechanical
| Introduction |  |
Standards Compliance and Certifications | |
Introduction | |
Technical Data | |
Ordering Information | |
Catalog Number Explanation | |
| Product Selection | |
Modifications | |
Accessories | |
Renewal Parts | |
Factory Options | |
Approximate Dimensions | |
Technical Terms
Adjustable operating range — Total span within which the contacts can be adjusted to trip and reset.
Trip setting — Higher temperature setting when the contacts transfer from their normal state to a changed state.
Reset setting — Lower temperature setting when the contacts return to their normal state.
Adjustable differential — Difference between the trip and reset values.
Minimum differential — When the differential is set to the lowest temperature difference between trip and reset.
Maximum differential — When the differential is set to the highest temperature difference between trip and reset.
Maximum temperature — The maximum temperature that can be applied to the bulb. This includes temperature override that may occur in the system. This rating must NOT be exceeded.
Operating range adjustment screw — This screw is used to adjust the trip setting by varying the force of the main spring.
Differential adjustment screw — This screw is used to adjust reset setting by varying the force of the differential blade spring.
Contact configuration — There are many types of contact configurations available. Bulletin 837 Temperature Controls are offered in a wide variety of contact configurations for both automatic operation and manual reset. See Contact Blocks — Trip temperature-indicating scales are supplied on controls with standard contact block..
Mounting — There are two methods of mounting temperature controls: remote or direct immersion.
Conversion factor — Temperatures given in Fahrenheit can be converted to Celsius using this equation: °C = 0.56 (°F –32°)
Temperatures given in Celsius can be converted to Fahrenheit using this equation: °F = (1.8 x °C) +32°
Figure 1
Graphics to illustrate technical terms
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Theory of Operation
Bulletin 837 Temperature Controls are designed to open or close electrical circuits in response to changes in temperature. Figure 2 is a simplified drawing of a temperature control. The bellows, bulb, and capillary are filled with a temperature-responsive liquid. The vapor pressure of the liquid increases as the temperature of the bulb increases. System temperature is converted to pressure through the bulb and capillary, which are connected to the control at the mounting stem. Pressure applied to the actuator changes in proportion to the temperature of the bulb. As temperature rises, the bellows exerts force on the main spring. When the threshold force of the main spring is overcome, it transfers the motion to the contact block and actuates the contacts — this is referred to as the trip setting. As temperature decreases, the main spring will retract. When the threshold force on the differential blade spring is overcome, the contacts will return to their normal state —this is referred to as reset setting. Varying the force of the main spring (by turning the operating range adjustment screw) determines when the contacts will trip. Varying the force on the secondary differential blade spring (by turning the differential adjustment screw) determines when the contacts will reset. Setting trip and reset determines control operation.
Figure 2
Basic mechanical structure
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Applications for Control
Temperature controls can be used to either control or monitor a machine or process. Figure 3 shows a typical control application. Here, temperature is controlled within predetermined high and low values. Figure 4 shows a typical monitoring application. Here, temperature is monitored between a high and low value, signaling when a preset limit has been exceeded.
Figure 3
Typical control application
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Figure 4
Typical monitoring application
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Control Settings
Allen-Bradley Temperature Controls are designed for ease of setting to help minimize installation time. Standard controls shipped from the factory are set at the maximum operating range and minimum differential. By following this simple two step process, the control can be set to the specific requirements for each application. See Figure 5.
Step 1 — Adjust trip setting
The trip setting is achieved by turning the operating range adjustment screw. Turn the screw counterclockwise to lower the trip setting or clockwise to raise the trip setting. The approximate trip setting is shown on the indicating scale.
Step 2 — Adjust reset setting
The reset setting is achieved by turning the differential adjustment screw counterclockwise to increase the differential or clockwise to decrease the differential.
Figure 5
Trip and reset adjustment
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Thermostat Wells
Thermostat wells are basically sealed tubes on one end with threads on the other that allow mounting directly into a system. Thermostat wells protect the bulbs and allow installing or removing controls for calibration without discharging or draining an entire system. The bulb of a temperature control is inserted into the well which is secured with a locking nut for standard bulb and capillary devices. Bulbs for armored capillary devices are secured with a sleeve nut and set screw to prevent the armor from sliding back exposing the capillary. The bulbs of direct immersion devices are secured with a set screw which is also used to mount the control. Thermostat wells are rated for 1000 psi at 600 °F. Thermostat wells used when mounting direct horizontal immersion controls will allow mounting the control in a confined space. These devices otherwise require an 11 in. swing diameter to secure the bulb into the system. See Thermostat Wells¬ .
Packing Glands
Packing glands are used when the application requires the bulb to be located deeper into a process than would be possible with a thermostat well. The glands provide a seal at any desired length along a standard capillary device. The bulb must be supported to resist damage from flow or turbulence within the system. The capillary of armored capillary devices can only be sealed at the small exposed section of capillary located at the bulb. Packing glands are not intended to seal around the armor. They are designed to withstand sealing pressures up to 50 psi. The packing gland cannot be assembled into a thermostat well. See Packing GlandsT .
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| Thermostat Wells | Packing Glands |
Bulb and Capillaries
Copper bulbs and capillaries are supplied for lower temperature ranges. Stainless steel is used for temperatures above 260 °F. Stainless steel is also available on lower ranges for more corrosive applications. The length of the standard capillary is 6 feet, but non-standard capillaries are available ranging from several inches up to 105 feet.
Armor
Bronze or stainless steel armor is available for added protection of the capillary. See Modifications on Tamper-Resistant Adjustment for ordering instructions.
Capillary Bending Radius
Copper and Stainless Steel —
0.5 in. (12.7 mm) minimum
with Bronze and Stainless Steel Armor —
2 in. (50.8 mm) minimum
Direct Immersion
Horizontal and vertical immersion devices are used when the controls are required to be mounted directly on the machine or in a process.
Standard Contact¬
Contact Operation
Contact blocks are single-pole, double-throw and can be wired to open or close on increasing or decreasing temperature.
Non-Inductive Ratings
5 A, 240V
3 A, 600V
Control Circuit Ratings
AC — 125 VA, 24…600V
DC — 57.5 VA, 115…230V
Standard Contact Wiring
Configuration
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Repeat Accuracy
The vapor pressure technology used in Bulletin 837 controls to sense temperature provides an exceptionally long operating life. High quality chemicals and rigid control during manufacturing provide a typical repeat accuracy of ±2 °F. Repeat accuracy is based on percent of maximum range, evaluated from test data and calculated using the formula per ICS 2-225 standards.
Special Controls
A large number of unlisted catalog modifications and complete devices are available for specific and OEM applications. Special controls and modification service is available to meet many applications unique to the OEM market.
Please consult your local Rockwell Automation sales office or Allen‑Bradley distributor for assistance with specific modified controls and accessories.
Temperature Range
The temperature range for the mechanism at +32 °F (0 °C) or below is based on the absence of freezing moisture, water or other fluids that may solidify and impede the operation of the control. Temperature ratings are as follows:
| Operating: |
–22… +150 °F (–30…+66 °C) |
| Storage: |
–22…+200 °F (–30…+93 °C) |
Factory-Set Temperature Controls
Rockwell Automation will factory set temperature controls to customer-specified values. Unspecified temperature controls shipped from the factory are set at the maximum operating range and minimum differential. See Factory Options, Factory Options.
Application Note
When the ambient temperature surrounding the mechanism of the temperature control approaches 30 °F (-1.1 °C) on either side of the setting, a cross-ambient type control should be used. This will protect against false temperature-sensing, as the bellows within the mechanism may otherwise respond to changes in temperature. Cat. Nos. 837-A3 and 837-A4 bulb and capillary Types, all 837-V direct vertical immersion, and all 837-H direct horizontal immersion devices are cross-ambient.
When the bulb of cross-ambient bulb and capillary controls 837-A3 and 837-A4 is to be mounted vertically, the capillary end of the bulb should always be positioned higher than the termination end of the bulb.
When mounting the bulb horizontally, the word “TOP” stamped near the capillary of the bulb should be positioned upward toward the 12 o' clock position. The capillary end of the bulb should never be higher than the termination end of the bulb. The direct vertical immersion devices in the catalog series 837-V are conventionally mounted with the bulb downward, below the mechanism.
They must not be mounted with the bulb up. Since the horizontal immersion device is not available in a Type 4 & 13 enclosure, the corresponding vertical immersion device can be used. When the vertical immersion device is mounted horizontally, the word “TOP” stamped on the mounting thread “hex” should point upward toward the 12 o' clock position.
The direct horizontal Immersion devices, in catalog series 837-H should always be mounted with the mechanism above the bulb. The word “TOP” stamped on the mounting thread “hex” should point upward toward the 12 o' clock position. Cat. No. 837-A2 is not cross-ambient and should not be used if the ambient temperature approaches or crosses over the set point as false temperature may occur.
Consult your local Rockwell Automation sales office or Allen-Bradley distributor for assistance on special applications.
¬ NEMA does not rate contacts to switch low-voltage and current. Bulletin 837 Styles A, H and V Temperature Controls are supplied with silver contacts. The devices are designed to deliver high force snap action to the contacts. This provides exceptional contact fidelity at 24V DC I/O card current level entry when the integrity of the enclosure is maintained.