Why Capacitance
One of the questions we get asked frequently is why use capacitance? Resistive sensors have been used for a long time…so why change? Why now?
Need for Capacitive Load Cells?
- a. It is the ability of a system to store charge. So if you take a set of parallel plates and apply a potential difference to it (Voltage), then for a brief time interval, electrons move from one plate to the other (a small current is generated) until it reaches a state of equilibrium (the current stops). The charge gets stored between the two parallel plates
- b. The amount of charge that can stored (its Capacitance) depends on the area between the plates, the distance between the plates and the dielectric constant between the plates.
- c. The formula for the Capacitance of the system can be shown as:
- C = Er*E0*A/d where Er is the dielectric Constant, E0 is the Permittivity of free space, A is the area of overlap between the plates and d is the gap between the plates
- For Air, Er=1 and E0 is a constant equal to 0.00854 picoFarad/mm
- So if you have two small overlapping discs of radius=5.6 mm and the gap between them equal to 0.25 mm, then the Capacitance of the system- C - is given by C = (1.0)*(0.00854)*(3.14159)*(5.6)2/(0.25) or 3.4 pF
- If the gap between the plates changes to 0.17 mm then the capacitance increases to 4.9 pF
- That is a change of 1.5 on 3.4 or 44.11%
However, note that, despite these advantages, capacitive load cells may not always be appropriate for monitoring applications that require high accuracies over long periods of time and when used in environments with changing temperatures and moist . We recommend using the capacitive load cells for applications that require a quick measurement where the initial conditions can be zeroed out and where the environment is maintained at steady room temperature and humidity conditions. Please consult Loadstar Sensors for advice on the most appropriate sensor for your application.
iLoad Series
iLoad
Low Profile Digital Load Cell with UART/USB Output
Capacities: 50 lb, 100 lb, 250 lb, 500 lb
Size: Dia 3 inch, 0.5 inch high
Accuracy Class: 0.25% of Full Scale
Compensated Temp Range: 20C to 30C
iLoad TR
Tilt Resistant Digital Load Cell with UART/USB Output
Capacities: 10 lb, 50 lb, 100 lb
Size: Dia. 3 inch, 1 inch high
Accuracy Class: 0.25% of Full Scale
Compensated Temp Range: 20C to 30C
iLoad Pro
Digital Load Cell with UART/USB Output
Capacities: 50 lb, 100 lb, 250 lb, 500 lb, 1K lb, 2.5K lb, 5K, 10K lb
Size: Dia 3.25 inch, 0.5 inch high
Accuracy Class: 0.25% to 1% of FS
Compensated Temp Range: 20C to 30C
iLoad Flex
Thin Flexible Miniature Load Cell with UART/USB Output
Capacities: 10 lb
Size: Dia. 10 mm, 3 mm high
Accuracy Class: 1-2% of Full Scale
Operating Temp Range: 20C to 30C
iLoad Mini
The smallest, thinnest capacitive load cell we offer
Capacities: 10 lb, 50 lb, 100 lb, 200 lb
Size: Dia. 1.25 inch, 0.25 inch high
Accuracy Class: 0.5% of Full Scale
Compensated Temp Range: 20C to 30C
iLoad Mini Stud
The mini load cell for tension/universal
Capacities: 10 lb, 50 lb, 100 lb, 200 lb
Size: Dia. 1.25 inch, 0.8 inch high
Accuracy Class: +/- 0.5% tp +/- 1% of Full Scale
Compensated Temp Range: 20C to 30C
iLoad Mini Pro
Low Profile Digital Load Cell with UART/USB Output
Capacities: 50 lb, 100 lb, 250 lb, 500 lb
Size: Dia 3 inch, 0.5 inch high
Accuracy Class: 0.25% of Full Scale
Compensated Temp Range: 20C to 30C
iLoad Mini Pro Stud
Digital Load Cell with UART/USB Output
Capacities: 50 lb, 100 lb, 250 lb, 500 lb, 1K lb, 2.5K lb, 5K, 10K lb
Size: Dia 3.25 inch, 0.5 inch high
Accuracy Class: 0.25% to 1% of FS
Compensated Temp Range: 20C to 30C
Comparison of Capacitive Load Cells
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| iLoad Mini Load Cell |
iLoad Mini Load Cell |
iLoad Mini Pro Load Cell |
iLoad Mini Pro Load Cell |
iLoad Low Profile Digital or Analog |
iLoad TR Digital or Analog |
iLoad Pro Digital or Analog |
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| Diameter | 1.25 in. | 1.25 in. | 2 in. | 2 in. | 3 in. | 3 in. | 3.25 in. to 5 in. |
| Height | 0.25 in. | 0.25 in. | 0.8 in. | 1.925 in. | 0.5 in. | 1.2 in. | 0.66-0.90 in. |
| Capacity | 10, 50, 100 & 200 lb. | 10, 50, 100 & 200 lb. | 500, 1K, 2.5K, 5K, 10K lb. | 500, 1K, 2.5K, 5K, 10K lb. | 50, 100, 250 & 500 lb. | 10, 50, & 100 lb. | 50, 100, 250, 500, 1K, 2.5K, 5K, 10K lb. |
| Best Accuracy* | ± 0.5% of FS | ± 0.5% of FS | ± 1% of FS | ± 1% of FS | ± 0.25% of FS | ± 0.25% of FS | ± 0.25% of FS |
| Mode of Use | Compression or Tension or Universal |
Compression Only | Compression Only | Compression or Tension or Universal |
Compression Only | Compression or Tension or Universal |
Compression or Tension or Universal |
| Cable Strain Relief | No (USB Type MiniB) |
No (USB Type MiniB) |
Yes (USB Type MiniB) |
Yes (USB Type MiniB) |
No (USB Type A) |
Yes (USB Type A) |
Yes (USB Type A) |
| Signal Conditioner | DQ-1000 or DQ-4000 or DS-4000 |
DQ-1000 or DQ-4000 or DS-4000 |
DQ-1000 or DQ-4000 or DS-4000 |
DQ-1000 or DQ-4000 or DS-4000 |
Built in to Load Cell |
Built in to Load Cell |
Built in to Load Cell |
| Output Options | Frequency (base), Serial TTL or USB (with DQ-1000) |
Frequency (base), Serial TTL or USB (with DQ-1000) |
Frequency (base), Serial TTL or USB (with DQ-1000) |
Frequency (base), Serial TTL or USB (with DQ-1000) |
Serial TTL or USB | Serial TTL or USB | Serial TTL or USB |
| Off Center Loading Compensation |
No (Force applied Axially) |
No (Force applied Axially) |
No (Force applied Axially) |
No (Force applied Axially) |
No (Force applied Axially) |
Yes (Can handle small off center loads) |
No (Force applied Axially) |
| Compatible Display | DS-3000-Pro-1 or DS-3000-Pro-4 |
DS-3000-Pro-1 or DS-3000-Pro-4 |
DS-3000-Pro-1 or DS-3000-Pro-4 |
DS-3000-Pro-1 or DS-3000-Pro-4 |
DS-3000-Pro-1 or DS-3000-Pro-4 |
DS-3000-Pro-1 or DS-3000-Pro-4 |
DS-3000-Pro-1 or DS-3000-Pro-4 |
| *With TARE at room temperature | |||||||
