问题 问答题 简答题

为什么电子式标准电能表的测量方式大多采用热电转换型或时分割乘法器型?

答案

参考答案:

热电转换型和时分割乘法器型具有精度高、成本低、启动电流小、电磁兼容性好、外磁场影响小等特点。尤其是热电转换型的电能表,在很低的功率因数和带很大波形畸变的电路中测量精确,而时分割乘法器型则具有较低的温度漂移和时间漂移。因此大多数标准电能表的测量方式采用热电转换型或时分割乘法器型。

单项选择题
单项选择题

Yellowstone Weather


Yellowstone National Park is at high altitude. Most of the park is above 7,500 feet (2,275 meters).
Yellowstone’s weather is unpredictable. In summer, it may be warm and sunny with temperatures in the high 70F. At night in any given month, the temperature may drop close to freezing. So it is best to come prepared for cold evenings and mornings, especially if you are camping or hiking. When you leave your campsite, please leave it prepared for possible thundershowers and wind.
A sunny warm day may become fiercely stormy with wind, rain, sleet and sometimes snow. Without enough clothing, an easy hike or boat trip can turn into a battle for survival.
Seasonal Weather Information
Spring
Cold and snow continue into May, although temperatures gradually climb Early in spring, daytime temperatures average in the 40F to 50F; by late May and June, they may reach the60F and 70F. Nighttime lows fall below freezing.
Summer
Daytime temperatures are usually in the 70F, occasionally reaching the 80F in the lower elevations (高度). Nights are cool, temperatures may drop in the 40F and 30F—sometimes even the 20F. June can be cool and rainy; July and August tend to be somewhat drier, although afternoon thundershowers are common.
Fall
Weather can be pleasant, although temperatures average 10-20 degrees lower than summer readings. Nighttime lows can fall into the teens and lower. Snowstorms increase in frequency as the weeks go by or towards the end of the fall season.
Winter
Temperatures often stay near zero throughout the day, occasionally reaching high in the20F. Subzero nighttime lows are common. Annual snowfall averages nearly 150 inches in most of the park. At higher places, 200-400 inches of snow have been recorded.

Which of the following best describes Yellowstone’s weather

A.Yellowstone’s weather is generally changeable and it snows most of the year.
B.It’s neither too hot in summer nor too cold in winter.
C.Weather in fall is pleasant and temperatures never fall below freezing.
D.It’s pretty warm in the day and very cool at night throughout the year.