How accurate is die temperature using sd_temp_get()

[Antonio]

Hi,

I am measuring die temperature of the nRF51822 using sd_temp_get() at the timeout handler of the RTC1 timer every 2 seconds.

I am using the battery service for a quick test.

After dividing the result by 4 I am getting 39 C (0x27 at the master control panel) when the room temperature is 26.

Am I doing something wrong?

Thanks,

This is a piece of my code:

static void battery_level_update(void) { uint32_t err_code; int32_t p_temp; uint8_t temperature;

	err_code = sd_temp_get(&p_temp);
            APP_ERROR_CHECK(err_code);
	temperature = (uint8_t)(p_temp / 4) ;

err_code = ble_bas_battery_level_update(&m_bas, temperature);
if ((err_code != NRF_SUCCESS) &&
    (err_code != NRF_ERROR_INVALID_STATE) &&
    (err_code != BLE_ERROR_NO_TX_BUFFERS) &&
    (err_code != BLE_ERROR_GATTS_SYS_ATTR_MISSING)
)
{
    APP_ERROR_HANDLER(err_code);
}

}

[Antonio]

Additional info: I am using the PCA10004 on top of the nRF6310.

[FormerMember]

The reason for this higher temperature reported is the activity that the chip is doing, especially when developing code. The temperature measured is of the IC die, which tends to get warm if not sleeping adequately. With processor running and periodic RF activity I've seen 55-60 C.

[Antonio]

Thank you Prithvi for your answer.

I thought the because of the low power the die basically ran cold.

I have the app sleeping using power_manage() in the main loop, the conn interval is every 500ms w/0 latency, and the timer fires every 2 seconds. I would think that, unless I am doing something wrong, it is sleeping more than 90% of the time. I also took of the DEBUG_NRF_USER flag and the SWI connector in case it was doing something that I would not be aware.

[FormerMember]

Well, the datasheet says that the temperature sensor peripheral is +/- 4 C accurate in its measurement. I was also surprised when i first saw it showing a lot more than room temperature. As an experiment, you could unplug it for sometime so that it is in room temperature so that you can see if the value increases after running for a while.

[Salman]

I am having the same issue, I am getting 39 or some times 40 but my room temperature is 28.