Load Cells and Signal Conditioners


#1

Load cells (usually strain guages)measure force. They may either have an internal amplifier, or require an external amplifier. An internal, or integral, amplifier may provide advantages such as fewer componenets, lower total cost, and possibly reduced noise, since an unamplified signal that is run to the external conditioner may be more susceptible to noise than an amplified signal.

For load cells with no integral amplifier, the millivolt signal from the load cell must be amplified with a signal conditioner in order to work with the RMC. For best resolution, the signal should be amplified to to ±10 V or 0-10 V, although ±5 V, 0-5 V, and 4-20 mA will work as well.

The bandwidth requirement of the signal conditioner depends on the system it is measuring. Slower systems (those that are large or have compliant loads) can use signal conditioners with bandwidths in the hundreds of Hz. Faster systems will require signal conditioners with bandwidths in the kHz range. If the bandwidth spec is given as a time constant, it should be 1 millisecond (equivalent to 160 Hz) or less, but 160 microseconds (equivalent to 1 kHz) or less is even better.

Delta is aware of the following load cells and signal conditioners that have good bandwidth and work with the RMCs:

Other signal conditioners with a bit slower response are available from:

For more details, or to suggest a product to be added to this list, send an email to support@deltamotion.com.


#2

Phoenix Contact makes a 1kHz and a 5Hz model. Do you have any experience with these, or recommendations based on the data sheets?

phoenixcontact.com/signal-le … _14920.htm


#3

Craig,

I am not aware that we have any experience with the Phoenix signal conditioners, but according to the specs, it appears they should work, especially the low-noise version.


#4

The bandwidth specification really refers to the cutoff frequency of the low-pass filter present in the signal conditioners, this enables it to remove noisy signals, read more here: https://tacunasystems.com/knowledge-base/ Imagine, the blades of a fan, as the speed increases it becomes difficult for your eyes to actually see these blades, they become jumbled up, so it is with signal conditioning. Noisy signals are very fast signals - high frequencies - and they interfere with the normal useful signal, so the filter helps to ensure that only the useful signals are present at the output, by cutting off higher frequencies.