How to Choose the Right Thermocouple Compensating Leads

Three crucial phases are involved in selecting the appropriate thermocouple compensating leads for hot runner systems: matching the thermocouple number, choosing the appropriate accuracy class, and adjusting to environmental requirements. The precise approach is as follows:

1. The first step is to strictly match the thermocouple number (this is an important prerequisite; a mismatch will lead to failure). The thermocouple number and the thermocouple number in the hot runner system must match exactly. This serves as the basis for selection:

The K-type hot runner thermocouple is the most widely used type: Choose the KX-type extended compensating lead (X stands for extended type; X is favored and has far greater accuracy than the C-type compensating lead). The J-type thermocouple is used in some imported European and American hot runner systems: Choose the extended compensating lead of the JX type. The T-type thermocouple is utilized in certain low-temperature situations: Choose the extended compensating lead of the TX type. It is strictly forbidden to mismatch, and regular copper wire cannot be replaced in its place. A predetermined temperature measurement deviation of 5–15°C will be introduced by the mismatch.

2. Step 2: Determine the Accuracy Grade in Light of Production Needs

Standard and precision grades are used for compensating leads. Select based on the requirements for injection molding accuracy:

Conventional Injection Molding/Ordinary Hot Runner: Standard grade is adequate and less expensive.

High Temperature Injection Molding: Precision grade is chosen, the compensation tolerance is lowered from ≤2°C to ≤1°C, and the accuracy is improved. Precision Injection Molding (product tolerance ≤0.01mm).

3. Step 3: Consider the Installation Environment When Choosing Material and Structure

Dimensions of Selection

Selection Criteria

Material for Insulation

Cold end ambient temperature ≤70°C: Use inexpensive PVC insulation;

If the ambient temperature is more than 70°C and the cold end is close to the hot runner, choose non-aging fluoroplastic insulation that can withstand temperatures up to 200°C.

Structural Conditions

Shielded compensating leads must be chosen to separate electromagnetic interference and prevent erratic temperature signal changes in hot runners near heating coils and injection molding motors.

A Brief Overview of Hot Runner Situations

Type of Hot Runner

Suggested Choice

Traditional Ordinary Hot Runner (K-type Thermocouple)

KX Standard Grade

Shielded PVC Insulation Type

KX Precision Grade Fluoroplastic Insulation Shielded Type Precision/High Temperature Hot Runner (Type K Thermocouple)

JX Precision Grade Fluoroplastic Insulation Shielded Type Imported Hot Runner with Type J Thermocouple