2 sensors, add delay between each reading

Question

I have two temperature sensors, an MCP9808 and a DS18B20, connected to an arduino and I've read that it could be advantageous to set a small delay between temperature readings. What I wonder is where I should set the delay, in the setup function:

tempsensor.begin();                           //initialize communication with mcp9808
sensors.begin();                              //initialize communication with dc18b20
readSensors();     

or the readSensors function?:

temp = tempsensor.readTempC();              //read current temperature and save value inside "temp"
sensors.requestTemperatures();              // Send the command to get temperatures
temp2 = sensors.getTempCByIndex(0);

As you can probably tell I am very new to all of this, intuition tells me that I should set the delay within the readSensors function.

Any alternative suggestions about how I should be readings temperature data from two different sensors connected to one arduino would be appreciated.

EDIT
after re-reading question and based on first answer I haven't made it unequivocally clear my intention; I want to delay the time between the mcp9808 and the ds18b20 temperature readings, so that it waits X seconds between each. I have read that this may help to reduce noise.

Answer 1

The essence of your question is actually about managing processor to processor communications. As the temperature sensors you have chosen appear as peripheral processors which communicate to your processor over SMBus (MCP9808) or 1-Wire bus (DS18B20).

Both temperature sensors actually abstract you from the details of (likely) thermistor Analog to Digital Conversion (ADC) sampling and (likely) exponential averaging over multiple samples in order to reduce noise by providing a digital communication interface. As you can see, there may be many steps taken before the temperature data is available over the digital communication interface. Each step takes a finite amount of time.

In almost all cases there is a microprocessor busy at work inside the temperature probe. How well that processor's code is written dictates how much you can (skip reading the MCP9808 and DS18B20 specification sheet(s) and) "abuse" the protocol.

If you ask for the data faster then the temperature probe can obtain a new sample, in the best case, it is likely you will be supplied with duplicate values or values clearly designated as errors. In the worst case, you may get back incorrect values indistinguishable from normal values. Read the specification sheets and consider the source of the parts.

All this said, it may be that the 2 libraries you have chosen to use are not compatible. Yes, one library is using the SMBus / I2C approach and the other is using the 1-Wire bus approach. However, if both libraries use any single Arduino resource (for example a hardware timer or a hardware interrupt) at the same time, they may interfere with one another.

To test this, comment out the instantiation and code for one of the approaches and see if the other begins working as you expected in the first place. Then repeat the experiment commenting out the other.

In the end, it is almost always better to use as few libraries as possible when assembling software for an Arduino. There may be some effort to make some libraries work together. But it is impractical to test all library combinations. For this specific case, using several temperature devices of the same type (all using the same serial bus) and assigning different addresses to each would allow you to restrict your self to only including / using one library.

Answer 2

I've read that it could be advantageous to set a small delay between temperature readings

Although temperature is typically a measure that changes slowly in time, there is nothing in programming/device side preventing you from making readings in short intervals; unless this added time is necessary to prevent issues on other tasks, but so it should be not related to that.