The cores of separate core type LVDTs are threaded internally at both ends for easy attachment to non-magnetic core rods. While core rods, typically, are easily constructed by the user to suit a wide variety of applications, Macro Sensors provides a wide assortment of Core Rod Connecting Kits that include pre-fabricated core connecting rods and accessories that simplify installation of separate core LVDTs. Macro Sensors core rods are made to match the core diameters and the internal core thread of standard Macro Sensors separate core LVDTs and are available in a variety of lengths. A diagram of a Core Rod Connecting Kit and its included components is shown below.
Core Rod Connecting Kit Diagram
Determining Minimum Core Rod Length
As shown in the diagram above, one end of the core connecting rod (Item 1) is internally threaded for attachment to the LVDT core using a socket head set screw (Item 4). The other end is externally threaded for easy attachment to the device being measured (using the jam nuts provided, Item 2), with the length of the thread (LL) allowing a certain amount of setup adjustment. The length of the unthreaded portion of the connecting rod (L) must be sufficient to allow movement of the core through the LVDT's full range of measurement. More specifically, when the core (with the connecting rod attached) is at the far limit of it's range (toward the end of the LVDT opposite the end from which the core rod is inserted), there should be enough of the externally threaded end of the core connecting rod extending from the LVDT to provide the necessary amount of adjustment. In this position, the length of the core rod extending should be greater than or equal to the threaded length of the rod (LL). The formulas below provide an easy way to calculate the minimum unthreaded length (L) of the core connecting rod.
Minimum Core Rod Length for AC or DC LVDTs with ± Ranges
To calculate the minimum unthreaded length (L) of the core connecting rod for AC or DC LVDTs, use the formula:
L = N + (R - C)/2
where N = distance of the null point from the end of the LVDT, R = the full range of the LVDT, and C = the length of the LVDT core. These dimensions can be obtained from the LVDT's individual web page or data sheet. Note that if the range is given as "± x inches", the full range of the LVDT (R) is equal to 2x.
Minimum Core Rod Length for Single-Ended DC or Loop Powered LVDTs with Non- ± Ranges
To calculate the minimum unthreaded length (L) of the core connecting rod for single-ended DC or loop powered LVDTs with non- ± ranges, use the formula:
L = S + R - (C/2)
where S = distance of the core position at the beginning of the range (zero output position) from the end of the LVDT, R = the full range of the LVDT, and C = the length of the LVDT core. These dimensions can also be obtained from the LVDT's individual web page or data sheet. Note that on some older data sheets that the "S" dimension is shown as "Z."
Selecting the Correct Core Rod Connecting Kit For Your LVDT
The first step in selecting the correct Core Rod Connecting Kit for your separate core LVDT is to identify the basic kit number from the tables below. If your LVDT has a standard threaded core, be sure to select the kit number from Table #1 for standard threaded cores. If your LVDT has a metric threaded core, be sure to select the kit number from Table #2 for metric threaded cores.
Table 1 - Core Rod Connecting Kits For LVDTs with Standard Threaded Cores
| LVDT Series | Use Core Rod Connecting Kit | Rod Diameter "D" |
External Thread "T" |
Internal Thread Tapping "TT" |
Set Screw "SS" |
| CD 375 | Core Rod Kit 110 (1-72 Thd) | 0.110" | 4-40 UNC | 1-72 UNF | 1-72 X 3/8" |
| DC 750 | Core Rod Kit 188 (4-40 Thd) | 0.188" | 10-32 UNF | 4-40 UNC | 4-40 X 1/2" |
| HLR 750 | Core Rod Kit 188 (4-40 Thd) | 0.188" | 10-32 UNF | 4-40 UNC | 4-40 X 1/2" |
| HSA/HSAR 750 | Core Rod Kit 188 (4-40 Thd) | 0.188" | 10-32 UNF | 4-40 UNC | 4-40 X 1/2" |
| HSD/HSDR 750 | Core Rod Kit 188 (4-40 Thd) | 0.188" | 10-32 UNF | 4-40 UNC | 4-40 X 1/2" |
| HSE/HSER 750 | Core Rod Kit 188 (4-40 Thd) | 0.188" | 10-32 UNF | 4-40 UNC | 4-40 X 1/2" |
| HSI/HSIR 750 | Core Rod Kit 188 (4-40 Thd) | 0.188" | 10-32 UNF | 4-40 UNC | 4-40 X 1/2" |
| HSTA/HSTAR 750 | Core Rod Kit 188 (4-40 Thd) | 0.188" | 10-32 UNF | 4-40 UNC | 4-40 X 1/2" |
| PR 750 | Core Rod Kit 250 (6-40 Thd) | 0.250" | 1/4-28 UNF | 6-40 UNF | 6-40 X 1/2" |
| PR 812 | Core Rod Kit 250 (6-40 Thd) | 0.250" | 1/4-28 UNF | 6-40 UNF | 6-40 X 1/2" |
| SE 750 | Core Rod Kit 188 (4-40 Thd) | 0.188" | 10-32 UNF | 4-40 UNC | 4-40 X 1/2" |
| SI 750 | Core Rod Kit 188 (4-40 Thd) | 0.188" | 10-32 UNF | 4-40 UNC | 4-40 X 1/2" |
| SQ 1250 | Core Rod Kit 250 (6-40 Thd) | 0.250" | 1/4-28 UNF | 6-40 UNF | 6-40 X 1/2" |
Table 2 - Core Rod Connecting Kits For LVDTs with Metric Threaded Cores
| LVDT Series | Use Core Rod Connecting Kit | Rod Diameter "D" |
External Thread "T" |
Internal Thread Tapping "TT" |
Set Screw "SS" |
| CD 375 | Core Rod Kit M110 (M2 Thd) | 2.80 mm | M3 X 0.5-6g | M2 X 0.4-6h | M2 X 10 mm |
| DC 750 | Core Rod Kit M188 (M3 Thd) | 4.77 mm | M5 X 0.8-6g | M3 X 0.5-6h | M3 X 13 mm |
| HLR 750 | Core Rod Kit M188 (M3 Thd) | 4.77 mm | M5 X 0.8-6g | M3 X 0.5-6h | M3 X 13 mm |
| HSA/HSAR 750 | Core Rod Kit M188 (M3 Thd) | 4.77 mm | M5 X 0.8-6g | M3 X 0.5-6h | M3 X 13 mm |
| HSD/HSDR 750 | Core Rod Kit M188 (M3 Thd) | 4.77 mm | M5 X 0.8-6g | M3 X 0.5-6h | M3 X 13 mm |
| HSE/HSER 750 | Core Rod Kit M188 (M3 Thd) | 4.77 mm | M5 X 0.8-6g | M3 X 0.5-6h | M3 X 13 mm |
| HSI/HSIR 750 | Core Rod Kit M188 (M3 Thd) | 4.77 mm | M5 X 0.8-6g | M3 X 0.5-6h | M3 X 13 mm |
| HSTA/HSTAR 750 | Core Rod Kit M188 (M3 Thd) | 4.77 mm | M5 X 0.8-6g | M3 X 0.5-6h | M3 X 13 mm |
| PR 750 | Core Rod Kit M250 (M4 Thd) | 6.35 mm | M6 X 1.0-6g | M4 X 0.7-6h | M4 X 13 mm |
| PR 812 | Core Rod Kit M250 (M4 Thd) | 6.35 mm | M6 X 1.0-6g | M4 X 0.7-6h | M4 X 13 mm |
| SE 750 | Core Rod Kit M188 (M3 Thd) | 4.77 mm | M5 X 0.8-6g | M3 X 0.5-6h | M3 X 13 mm |
| SI 750 | Core Rod Kit M188 (M3 Thd) | 4.77 mm | M5 X 0.8-6g | M3 X 0.5-6h | M3 X 13 mm |
| SQ 1250 | Core Rod Kit M250 (M4 Thd) | 6.35 mm | M6 X 1.0-6g | M4 X 0.7-6h | M4 X 13 mm |
After you have identified the proper Core Rod Connecting Kit, calculate the minimum unthreaded length (L) of the rod needed for your specific LVDT, using the formulas in the section above, "Determining Minimum Core Rod Length." Obtain the null or zero output dimensions, range, and core length from the LVDT web page or data sheet. The "LVDT Series" links in the tables above will take you directly to the page for the corresponding LVDT.
After establishing the minimum unthreaded length (L), identify the proper model number of the core connecting rod for your Core Rod Connecting Kit from the tables below. When ordering, make sure that you identify both the proper Core Rod Kit (standard or metric) and the Model Number of the core rod that has a length (L) that is greater than or equal to the "L" value you calculated for yout LVDT. If you cannot find a core rod that meets your exact requirements, please do not hesitate to contact Macro Sensors.
Core Rod Dimensions for Macro Sensors Core Rod Connecting Kits
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Standard Thread
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Metric Thread
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