# Scaling a +/-5V Signal to 200mV for a Torque Sensor

• zekester
In summary, the conversation discusses the need to scale a +/-5 voltage signal from a torque sensor to a maximum input of 200 mV for display on a panel meter. The initial belief was that a simple voltage divider followed by a noninverting op-amp could accomplish this, but the mismatch between the negative and positive voltage signals caused uncertainty. It is suggested that a differential amplifier or a 2-point linear scaling feature on the panel meter could be used. It is also advised to have a stable power supply and proper decoupling when dealing with real-life data. Using 1% tolerance resistors and a low-distortion buffer amplifier are recommended for scaling the output voltage.
zekester
i am taking a +/-5 voltage signal is supposed coming from a torque sensor. this is supposed to be equal to 100 N*m. However, -5.04 volts is actually equal to 100 N*m and 4.85 volts is actually equal to 100 N*m. I need to scale this signal to a maximum input of 200 mV for display on a panel meter. I was just going to use a voltage divider going into a noninverting op-amp, but I am not sure what to do now that I know the negative and positive voltage signals don't match, I was told a differential amplifier would work for this, however, I am not quite sure of how to accomplish this, any help would be appreciated.

A differential amp could work but is not required. Depending how much current you have available from the sensor and where you are connecting it, a simple two resistor voltage divider would suffice.

If you want to use an op-amp, then a non-inverting amp configuration could follow the voltage divider network. But you would need a positive and a negative power supply connection for the IC.

Many panel display units have built in scalling features. I am familiar with the Omron http://www.omron247.com/Industrial-Automation/Store/OmronFamilyView_10051_10051_-1_11921" It allows for a 2 point linear scaling. This may be a more documentable solution.

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Most of the sensors provide an output that is offseted by Vcc/2. Is your sensor based on the same method?

Measuring real life data is not an easy task to accomplish. I've been dealing with this kind of circuits for a couple of years now, so here is my advice for best results:

1. Good power supply with stable output voltage! (output voltage variations are allways caused by unstable powersupply) Hense, use some stabilizing circuits.

2. DECOUPLING DECOUPLING DECOUPLING ! ! ! Place decoupling capacitors as close to the sensor IC as possible, avoid ground layer around the IC etc. Short distances between the circuits = GOOD! Long distances = BAD (remember transmission line theory) parasitics etc. etc.

3. When dealing with unmatched output (i.e 5,04 & 4,85V) you can either offset (by applying the dc to the output) the input (so the output will swing between $$\frac{5,04+4,85}{2}$$) or you can use microcontroller or some other means to do so. Just be shure that those unmatched swings are not caused by the way you've configured the IC.

4. Use 1% resistors, if your circuit is modeled correctly and psu variations has nothing to do with unmatched output, then problem can be that you're using >=5% resistors. When modelling sensor-circuits allways use 1% tolerance resistors, such as 1206 or lower series.

Now, for for scaling the output voltage down, I would suggest a divider network followed by a low-distortion buffer amplifier so the circuits after buffer would not load the divider, hence not affecting your read-outs.

## 1. How do I scale a +/-5V signal to 200mV for a torque sensor?

Scaling a signal involves manipulating the input range of a signal to match the desired output range. To scale a +/-5V signal to 200mV for a torque sensor, you will need a voltage divider circuit. This circuit consists of two resistors, with one connected to the input signal and the other connected to ground. The output voltage is then taken from the connection between the two resistors. The values of the resistors can be calculated using the formula Vout = Vin * R2/(R1 + R2). By choosing appropriate resistor values, you can achieve a 200mV output signal from a +/-5V input signal.

## 2. Why is scaling necessary for a torque sensor?

Scaling is necessary for a torque sensor because it allows the sensor to accurately measure and report torque values within a specific range. Without scaling, the sensor may not be able to accurately read the torque being applied, leading to inaccurate measurements and potentially damaging the sensor.

## 3. Can I use a different method to scale the signal for my torque sensor?

Yes, there are multiple methods for scaling a signal for a torque sensor. One alternative method is using an instrumentation amplifier, which amplifies the difference between two input signals. Another method is using a microcontroller with an analog-to-digital converter (ADC) to read the input signal and then manipulate it to the desired output range.

## 4. How can I ensure the accuracy of the scaled signal for my torque sensor?

To ensure the accuracy of the scaled signal, it is important to use high-quality components for the voltage divider circuit. This includes using precision resistors with low tolerance values and a stable power supply. Additionally, you should calibrate the sensor after scaling to verify the accuracy of the readings.

## 5. Is there a maximum input signal range that can be scaled to 200mV for a torque sensor?

The maximum input signal range that can be scaled to 200mV for a torque sensor depends on the specific sensor and its capabilities. It is important to consult the sensor's datasheet to determine the maximum input voltage it can handle. If the input signal exceeds this range, it can damage the sensor or result in inaccurate readings.

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