✅ SOP: Selection of Correct Range for JUMO Thermostats

1. Purpose

To define a standard, foolproof method for selecting the correct temperature range of a JUMO thermostat so that:

• Switching is accurate and stable

• Control performance is repeatable and reliable

• Mechanical and electronic stress on the thermostat is minimized

• Customers don’t complain that “it switches late / early / randomly” 😄

2. Basic Principle (This is the Golden Rule 🏆)

The actual switching temperature MUST lie in the upper third of the selected thermostat range.

Why?

Because:

• Thermostats are most accurate and stable in the upper part of their scale

• Near the lower end:

  • Switching tolerance increases

  • Hysteresis becomes less predictable

  • Mechanical stress increases

• Near the upper third:

  • Best repeatability

  • Best long-term stability

  • Best switching accuracy

3. Definition: “Upper Third of Range”

If thermostat range is:

Tmin to Tmax

Then:

Upper third starts at:

And the setpoint should lie between:

Tupper_start and Tmax

4. Step-by-Step Selection Procedure

Step 1: Identify the Required Switching Temperature

From process or customer:

Example:
Switching required at = 120 °C

Step 2: List Available JUMO Thermostat Ranges

Example available models:

• 0…100 °C

• 0…150 °C

• 50…200 °C

• 0…300 °C

Step 3: Check Where the Setpoint Lies in Each Range

Let’s test 0…150 °C:

Upper third starts at:

✔ 120°C lies between 100…150 → GOOD choice

Test 0…300 °C:

Upper third starts at:

❌ 120°C is far below → BAD choice (poor accuracy & stability)

Step 4: Select the Smallest Range That Still Puts Setpoint in Upper Third

✅ Always choose the narrowest possible range that satisfies the rule.

So for 120°C:

✔ Best choice: 0…150°C
❌ Avoid: 0…300°C

5. Quick Decision Table

6. Engineering Reasons (For When Customer Asks “Why?”)

You can confidently say:

• Thermostat accuracy is not linear over the entire scale

• Mechanical spring / sensor system is most stable near upper working zone

• Operating near lower end causes:

  • Larger switching tolerances

  • More drift

  • More hysteresis variation

• Correct range selection:

  • Improves lifetime

  • Improves repeatability

  • Improves process stability

7. Mandatory Rule for Quotation & Ordering (Important for JUMO Sales)

❗ Never select a thermostat range just because it “covers” the temperature.
❗ Always check where the switching point lies inside the range.

8. One-Line Rule (For Your Internal Training Slides)

🧠 “The thermostat setpoint must always lie in the upper third of its scale — and the range should be as narrow as possible.”

9. Real-World Example (Use This in Training)

Customer wants:

Switch heater OFF at 90°C

Available ranges:

• 0…100°C → Upper third starts at 66°C → ✔ PERFECT

• 0…300°C → Upper third starts at 200°C → ❌ TERRIBLE